Add per-channel hybrid audio spread spectrum and env feature toggles

Spread spectrum v2: independent per-channel embedding with round-robin
bit distribution, preserving spatial stereo/surround mix. Adaptive chip
tiers (256/512/1024) trade capacity for lossy codec robustness. LFE
channel skipped for 5.1+ layouts. v2 header (20B) with backward-
compatible v0 decode fallback.

Environment toggles (STEGASOO_AUDIO, STEGASOO_VIDEO) gate audio/video
features for minimal builds (e.g. Raspberry Pi image-only). Values:
auto (default, detect deps), 1/true (force on), 0/false (force off).

Web UI fixes: accordion defaults to step 1 on load, chevron arrow
styling, required attribute toggling for audio carrier type switch,
"Images & Mode" renamed to "Reference, Carrier, Mode".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontends/web/app.py

@@ -146,6 +146,7 @@ sys.path.insert(0, str(Path(__file__).parent.parent.parent / "src"))
 
 import stegasoo
 from stegasoo import (
+    HAS_AUDIO_SUPPORT,
     CapacityError,
     DecryptionError,
     FilePayload,
@@ -463,6 +464,9 @@ def inject_globals():
         "is_admin": is_admin(),
         # NEW in v4.2.0 - Saved channel keys
         "saved_channel_keys": saved_channel_keys,
+        # NEW in v4.3.0 - Audio support
+        "has_audio": HAS_AUDIO_SUPPORT,
+        "supported_audio_formats": "WAV, FLAC, MP3, OGG, AAC, M4A" if HAS_AUDIO_SUPPORT else "",
     }
 
 
@@ -564,6 +568,14 @@ def allowed_image(filename: str) -> bool:
     return ext in {"png", "jpg", "jpeg", "bmp", "gif"}
 
 
+def allowed_audio(filename: str) -> bool:
+    """Check if file has allowed audio extension."""
+    if not filename or "." not in filename:
+        return False
+    ext = filename.rsplit(".", 1)[1].lower()
+    return ext in {"wav", "flac", "mp3", "ogg", "aac", "m4a", "aiff", "aif"}
+
+
 def format_size(size_bytes: int) -> str:
     """Format file size for display."""
     if size_bytes < 1024:
@@ -710,11 +722,15 @@ def generate():
                 if not qr_too_large:
                     qr_token = secrets.token_urlsafe(16)
                     cleanup_temp_files()
-                    temp_storage.save_temp_file(qr_token, creds.rsa_key_pem.encode(), {
-                        "filename": "rsa_key.pem",
-                        "type": "rsa_key",
-                        "compress": qr_needs_compression,
-                    })
+                    temp_storage.save_temp_file(
+                        qr_token,
+                        creds.rsa_key_pem.encode(),
+                        {
+                            "filename": "rsa_key.pem",
+                            "type": "rsa_key",
+                            "compress": qr_needs_compression,
+                        },
+                    )
 
             # v3.2.0: Single passphrase instead of daily phrases
             return render_template(
@@ -1001,6 +1017,37 @@ def api_check_fit():
         return jsonify({"error": str(e)}), 500
 
 
+@app.route("/api/audio-capacity", methods=["POST"])
+@login_required
+def api_audio_capacity():
+    """Get audio file capacity for steganography (v4.3.0)."""
+    audio_file = request.files.get("carrier")
+    if not audio_file:
+        return jsonify({"error": "No audio file provided"}), 400
+
+    try:
+        audio_data = audio_file.read()
+        result = subprocess_stego.audio_info(audio_data)
+
+        if not result.success:
+            return jsonify({"error": result.error or "Audio analysis failed"}), 500
+
+        return jsonify(
+            {
+                "success": True,
+                "sample_rate": result.sample_rate,
+                "channels": result.channels,
+                "duration": round(result.duration_seconds, 2),
+                "format": result.format,
+                "bit_depth": result.bit_depth,
+                "lsb_capacity": result.capacity_lsb,
+                "spread_capacity": result.capacity_spread,
+            }
+        )
+    except Exception as e:
+        return jsonify({"error": str(e)}), 500
+
+
 # ============================================================================
 # ENCODE
 # ============================================================================
@@ -1078,15 +1125,105 @@ def _run_encode_job(job_id: str, encode_params: dict) -> None:
 
         # Store result
         file_id = secrets.token_urlsafe(16)
-        temp_storage.save_temp_file(file_id, encode_result.stego_data, {
-            "filename": filename,
-            "embed_mode": embed_mode,
-            "output_format": dct_output_format if embed_mode == "dct" else "png",
-            "color_mode": dct_color_mode if embed_mode == "dct" else None,
-            "mime_type": output_mime,
-            "channel_mode": encode_result.channel_mode,
-            "channel_fingerprint": encode_result.channel_fingerprint,
-        })
+        temp_storage.save_temp_file(
+            file_id,
+            encode_result.stego_data,
+            {
+                "filename": filename,
+                "embed_mode": embed_mode,
+                "output_format": dct_output_format if embed_mode == "dct" else "png",
+                "color_mode": dct_color_mode if embed_mode == "dct" else None,
+                "mime_type": output_mime,
+                "channel_mode": encode_result.channel_mode,
+                "channel_fingerprint": encode_result.channel_fingerprint,
+            },
+        )
+
+        _store_job(
+            job_id,
+            {
+                "status": "complete",
+                "file_id": file_id,
+                "created": time.time(),
+            },
+        )
+
+    except Exception as e:
+        _store_job(
+            job_id,
+            {
+                "status": "error",
+                "error": str(e),
+                "created": time.time(),
+            },
+        )
+    finally:
+        cleanup_progress_file(job_id)
+
+
+def _run_encode_audio_job(job_id: str, encode_params: dict) -> None:
+    """Background thread function for async audio encode (v4.3.0)."""
+    progress_file = get_progress_file_path(job_id)
+
+    try:
+        _store_job(job_id, {"status": "running", "created": time.time()})
+
+        if encode_params.get("file_data"):
+            encode_result = subprocess_stego.encode_audio(
+                carrier_data=encode_params["carrier_data"],
+                reference_data=encode_params["ref_data"],
+                file_data=encode_params["file_data"],
+                file_name=encode_params["file_name"],
+                file_mime=encode_params["file_mime"],
+                passphrase=encode_params["passphrase"],
+                pin=encode_params.get("pin"),
+                rsa_key_data=encode_params.get("rsa_key_data"),
+                rsa_password=encode_params.get("key_password"),
+                embed_mode=encode_params["embed_mode"],
+                channel_key=encode_params.get("channel_key"),
+                progress_file=progress_file,
+                chip_tier=encode_params.get("chip_tier"),
+            )
+        else:
+            encode_result = subprocess_stego.encode_audio(
+                carrier_data=encode_params["carrier_data"],
+                reference_data=encode_params["ref_data"],
+                message=encode_params.get("message"),
+                passphrase=encode_params["passphrase"],
+                pin=encode_params.get("pin"),
+                rsa_key_data=encode_params.get("rsa_key_data"),
+                rsa_password=encode_params.get("key_password"),
+                embed_mode=encode_params["embed_mode"],
+                channel_key=encode_params.get("channel_key"),
+                progress_file=progress_file,
+                chip_tier=encode_params.get("chip_tier"),
+            )
+
+        if not encode_result.success:
+            _store_job(
+                job_id,
+                {
+                    "status": "error",
+                    "error": encode_result.error or "Audio encoding failed",
+                    "created": time.time(),
+                },
+            )
+            return
+
+        filename = generate_filename("stego_audio", ".wav")
+        file_id = secrets.token_urlsafe(16)
+        temp_storage.save_temp_file(
+            file_id,
+            encode_result.stego_data,
+            {
+                "filename": filename,
+                "embed_mode": encode_params["embed_mode"],
+                "carrier_type": "audio",
+                "mime_type": "audio/wav",
+                "channel_mode": encode_result.channel_mode,
+                "channel_fingerprint": encode_result.channel_fingerprint,
+            },
+        )
 
         _store_job(
             job_id,
@@ -1131,6 +1268,196 @@ def encode_page():
             rsa_key_file = request.files.get("rsa_key")
             payload_file = request.files.get("payload_file")
 
+            # Determine carrier type (v4.3.0)
+            carrier_type = request.form.get("carrier_type", "image")
+
+            if carrier_type == "audio":
+                # ========== AUDIO ENCODE PATH (v4.3.0) ==========
+                if not HAS_AUDIO_SUPPORT:
+                    return _error_response(
+                        "Audio steganography is not available. Install audio dependencies."
+                    )
+
+                if not ref_photo or not carrier:
+                    return _error_response("Both reference photo and audio carrier are required")
+
+                if not allowed_image(ref_photo.filename):
+                    return _error_response("Reference must be an image (PNG, JPG, BMP)")
+
+                if not allowed_audio(carrier.filename):
+                    return _error_response(
+                        "Invalid audio format. Use WAV, FLAC, MP3, OGG, AAC, or M4A"
+                    )
+
+                # Get form data
+                message = request.form.get("message", "")
+                passphrase = request.form.get("passphrase", "")
+                pin = request.form.get("pin", "").strip()
+                rsa_password = request.form.get("rsa_password", "")
+                payload_type = request.form.get("payload_type", "text")
+
+                embed_mode = request.form.get("embed_mode", "audio_lsb")
+                if embed_mode not in ("audio_lsb", "audio_spread"):
+                    embed_mode = "audio_lsb"
+
+                # Chip tier for spread spectrum (None = default)
+                chip_tier_str = request.form.get("chip_tier")
+                chip_tier = None
+                if chip_tier_str and chip_tier_str.isdigit():
+                    chip_tier = int(chip_tier_str)
+                    if chip_tier not in (0, 1, 2):
+                        chip_tier = None
+
+                channel_key = resolve_channel_key_form(request.form.get("channel_key", "auto"))
+
+                # Determine payload
+                if payload_type == "file" and payload_file and payload_file.filename:
+                    file_data = payload_file.read()
+                    result = validate_file_payload(file_data, payload_file.filename)
+                    if not result.is_valid:
+                        return _error_response(result.error_message)
+                    mime_type, _ = mimetypes.guess_type(payload_file.filename)
+                    payload = FilePayload(
+                        data=file_data,
+                        filename=payload_file.filename,
+                        mime_type=mime_type,
+                    )
+                else:
+                    result = validate_message(message)
+                    if not result.is_valid:
+                        return _error_response(result.error_message)
+                    payload = message
+
+                if not passphrase:
+                    return _error_response("Passphrase is required")
+
+                result = validate_passphrase(passphrase)
+                if not result.is_valid:
+                    return _error_response(result.error_message)
+                if result.warning:
+                    flash(result.warning, "warning")
+
+                ref_data = ref_photo.read()
+                carrier_data = carrier.read()
+
+                # Handle RSA key (same as image path)
+                rsa_key_data = None
+                rsa_key_pem = request.form.get("rsa_key_pem", "").strip()
+                rsa_key_qr = request.files.get("rsa_key_qr")
+                rsa_key_from_qr = False
+
+                if rsa_key_pem:
+                    if is_compressed(rsa_key_pem):
+                        rsa_key_pem = decompress_data(rsa_key_pem)
+                    rsa_key_data = rsa_key_pem.encode("utf-8")
+                    rsa_key_from_qr = True
+                elif rsa_key_file and rsa_key_file.filename:
+                    rsa_key_data = rsa_key_file.read()
+                elif rsa_key_qr and rsa_key_qr.filename and HAS_QRCODE_READ:
+                    qr_image_data = rsa_key_qr.read()
+                    key_pem = extract_key_from_qr(qr_image_data)
+                    if key_pem:
+                        rsa_key_data = key_pem.encode("utf-8")
+                        rsa_key_from_qr = True
+                    else:
+                        return _error_response("Could not extract RSA key from QR code image.")
+
+                result = validate_security_factors(pin, rsa_key_data)
+                if not result.is_valid:
+                    return _error_response(result.error_message)
+
+                if pin:
+                    result = validate_pin(pin)
+                    if not result.is_valid:
+                        return _error_response(result.error_message)
+
+                key_password = None if rsa_key_from_qr else (rsa_password if rsa_password else None)
+
+                if rsa_key_data:
+                    result = validate_rsa_key(rsa_key_data, key_password)
+                    if not result.is_valid:
+                        return _error_response(result.error_message)
+
+                # Build audio encode params
+                encode_params = {
+                    "carrier_data": carrier_data,
+                    "ref_data": ref_data,
+                    "passphrase": passphrase,
+                    "pin": pin if pin else None,
+                    "rsa_key_data": rsa_key_data,
+                    "key_password": key_password,
+                    "embed_mode": embed_mode,
+                    "channel_key": channel_key,
+                    "carrier_type": "audio",
+                    "chip_tier": chip_tier,
+                }
+
+                if payload_type == "file" and payload_file and payload_file.filename:
+                    encode_params["file_data"] = payload.data
+                    encode_params["file_name"] = payload.filename
+                    encode_params["file_mime"] = payload.mime_type
+                else:
+                    encode_params["message"] = payload
+
+                if is_async:
+                    job_id = generate_job_id()
+                    _store_job(job_id, {"status": "pending", "created": time.time()})
+                    _executor.submit(_run_encode_audio_job, job_id, encode_params)
+                    return jsonify({"job_id": job_id, "status": "pending"})
+
+                # Sync audio encode
+                if encode_params.get("file_data"):
+                    encode_result = subprocess_stego.encode_audio(
+                        carrier_data=carrier_data,
+                        reference_data=ref_data,
+                        file_data=encode_params["file_data"],
+                        file_name=encode_params["file_name"],
+                        file_mime=encode_params["file_mime"],
+                        passphrase=passphrase,
+                        pin=pin if pin else None,
+                        rsa_key_data=rsa_key_data,
+                        rsa_password=key_password,
+                        embed_mode=embed_mode,
+                        channel_key=channel_key,
+                        chip_tier=chip_tier,
+                    )
+                else:
+                    encode_result = subprocess_stego.encode_audio(
+                        carrier_data=carrier_data,
+                        reference_data=ref_data,
+                        message=payload,
+                        passphrase=passphrase,
+                        pin=pin if pin else None,
+                        rsa_key_data=rsa_key_data,
+                        rsa_password=key_password,
+                        embed_mode=embed_mode,
+                        channel_key=channel_key,
+                        chip_tier=chip_tier,
+                    )
+
+                if not encode_result.success:
+                    error_msg = encode_result.error or "Audio encoding failed"
+                    return _error_response(error_msg)
+
+                filename = generate_filename("stego_audio", ".wav")
+                file_id = secrets.token_urlsafe(16)
+                cleanup_temp_files()
+                temp_storage.save_temp_file(
+                    file_id,
+                    encode_result.stego_data,
+                    {
+                        "filename": filename,
+                        "embed_mode": embed_mode,
+                        "carrier_type": "audio",
+                        "mime_type": "audio/wav",
+                        "channel_mode": encode_result.channel_mode,
+                        "channel_fingerprint": encode_result.channel_fingerprint,
+                    },
+                )
+
+                return redirect(url_for("encode_result", file_id=file_id))
+
+            # ========== IMAGE ENCODE PATH (original) ==========
             if not ref_photo or not carrier:
                 return _error_response("Both reference photo and carrier image are required")
 
@@ -1356,16 +1683,20 @@ def encode_page():
             # Store temporarily
             file_id = secrets.token_urlsafe(16)
             cleanup_temp_files()
-            temp_storage.save_temp_file(file_id, encode_result.stego_data, {
-                "filename": filename,
-                "embed_mode": embed_mode,
-                "output_format": dct_output_format if embed_mode == "dct" else "png",
-                "color_mode": dct_color_mode if embed_mode == "dct" else None,
-                "mime_type": output_mime,
-                # Channel info (v4.0.0)
-                "channel_mode": encode_result.channel_mode,
-                "channel_fingerprint": encode_result.channel_fingerprint,
-            })
+            temp_storage.save_temp_file(
+                file_id,
+                encode_result.stego_data,
+                {
+                    "filename": filename,
+                    "embed_mode": embed_mode,
+                    "output_format": dct_output_format if embed_mode == "dct" else "png",
+                    "color_mode": dct_color_mode if embed_mode == "dct" else None,
+                    "mime_type": output_mime,
+                    # Channel info (v4.0.0)
+                    "channel_mode": encode_result.channel_mode,
+                    "channel_fingerprint": encode_result.channel_fingerprint,
+                },
+            )
 
             return redirect(url_for("encode_result", file_id=file_id))
 
@@ -1434,13 +1765,16 @@ def encode_result(file_id):
         flash("File expired or not found. Please encode again.", "error")
         return redirect(url_for("encode_page"))
 
-    # Generate thumbnail
-    thumbnail_data = generate_thumbnail(file_info["data"])
-    thumbnail_id = None
+    carrier_type = file_info.get("carrier_type", "image")
 
-    if thumbnail_data:
-        thumbnail_id = f"{file_id}_thumb"
-        temp_storage.save_thumbnail(thumbnail_id, thumbnail_data)
+    # Generate thumbnail only for images
+    thumbnail_data = None
+    thumbnail_id = None
+    if carrier_type != "audio":
+        thumbnail_data = generate_thumbnail(file_info["data"])
+        if thumbnail_data:
+            thumbnail_id = f"{file_id}_thumb"
+            temp_storage.save_thumbnail(thumbnail_id, thumbnail_data)
 
     return render_template(
         "encode_result.html",
@@ -1450,6 +1784,7 @@ def encode_result(file_id):
         embed_mode=file_info.get("embed_mode", "lsb"),
         output_format=file_info.get("output_format", "png"),
         color_mode=file_info.get("color_mode"),
+        carrier_type=carrier_type,
         # Channel info (v4.0.0)
         channel_mode=file_info.get("channel_mode", "public"),
         channel_fingerprint=file_info.get("channel_fingerprint"),
@@ -1464,9 +1799,7 @@ def encode_thumbnail(thumb_id):
     if not thumb_data:
         return "Thumbnail not found", 404
 
-    return send_file(
-        io.BytesIO(thumb_data), mimetype="image/jpeg", as_attachment=False
-    )
+    return send_file(io.BytesIO(thumb_data), mimetype="image/jpeg", as_attachment=False)
 
 
 @app.route("/encode/download/<file_id>")
@@ -1559,10 +1892,92 @@ def _run_decode_job(job_id: str, decode_params: dict) -> None:
         if decode_result.is_file:
             file_id = secrets.token_urlsafe(16)
             filename = decode_result.filename or "decoded_file"
-            temp_storage.save_temp_file(file_id, decode_result.file_data, {
-                "filename": filename,
-                "mime_type": decode_result.mime_type,
-            })
+            temp_storage.save_temp_file(
+                file_id,
+                decode_result.file_data,
+                {
+                    "filename": filename,
+                    "mime_type": decode_result.mime_type,
+                },
+            )
+            _store_job(
+                job_id,
+                {
+                    "status": "complete",
+                    "file_id": file_id,
+                    "is_file": True,
+                    "filename": filename,
+                    "file_size": len(decode_result.file_data),
+                    "mime_type": decode_result.mime_type,
+                    "created": time.time(),
+                },
+            )
+        else:
+            _store_job(
+                job_id,
+                {
+                    "status": "complete",
+                    "is_file": False,
+                    "message": decode_result.message,
+                    "created": time.time(),
+                },
+            )
+
+    except Exception as e:
+        _store_job(
+            job_id,
+            {
+                "status": "error",
+                "error": str(e),
+                "created": time.time(),
+            },
+        )
+    finally:
+        cleanup_progress_file(job_id)
+
+
+def _run_decode_audio_job(job_id: str, decode_params: dict) -> None:
+    """Background thread function for async audio decode (v4.3.0)."""
+    progress_file = get_progress_file_path(job_id)
+
+    try:
+        _store_job(job_id, {"status": "running", "created": time.time()})
+
+        decode_result = subprocess_stego.decode_audio(
+            stego_data=decode_params["stego_data"],
+            reference_data=decode_params["ref_data"],
+            passphrase=decode_params["passphrase"],
+            pin=decode_params.get("pin"),
+            rsa_key_data=decode_params.get("rsa_key_data"),
+            rsa_password=decode_params.get("rsa_password"),
+            embed_mode=decode_params.get("embed_mode", "audio_auto"),
+            channel_key=decode_params.get("channel_key"),
+            progress_file=progress_file,
+        )
+
+        if not decode_result.success:
+            _store_job(
+                job_id,
+                {
+                    "status": "error",
+                    "error": decode_result.error or "Audio decoding failed",
+                    "error_type": decode_result.error_type,
+                    "created": time.time(),
+                },
+            )
+            return
+
+        if decode_result.is_file:
+            file_id = secrets.token_urlsafe(16)
+            filename = decode_result.filename or "decoded_file"
+            temp_storage.save_temp_file(
+                file_id,
+                decode_result.file_data,
+                {
+                    "filename": filename,
+                    "mime_type": decode_result.mime_type,
+                },
+            )
             _store_job(
                 job_id,
                 {
@@ -1609,6 +2024,163 @@ def decode_page():
             stego_image = request.files.get("stego_image")
             rsa_key_file = request.files.get("rsa_key")
 
+            # Determine carrier type (v4.3.0)
+            carrier_type = request.form.get("carrier_type", "image")
+
+            if carrier_type == "audio":
+                # ========== AUDIO DECODE PATH (v4.3.0) ==========
+                if not HAS_AUDIO_SUPPORT:
+                    flash("Audio steganography is not available.", "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                if not ref_photo or not stego_image:
+                    flash("Both reference photo and stego audio are required", "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                if not allowed_image(ref_photo.filename):
+                    flash("Reference must be an image", "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                if not allowed_audio(stego_image.filename):
+                    flash("Invalid audio format", "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                passphrase = request.form.get("passphrase", "")
+                pin = request.form.get("pin", "").strip()
+                rsa_password = request.form.get("rsa_password", "")
+
+                embed_mode = request.form.get("embed_mode", "audio_auto")
+                if embed_mode not in ("audio_auto", "audio_lsb", "audio_spread"):
+                    embed_mode = "audio_auto"
+
+                channel_key = resolve_channel_key_form(request.form.get("channel_key", "auto"))
+
+                if not passphrase:
+                    flash("Passphrase is required", "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                ref_data = ref_photo.read()
+                stego_data = stego_image.read()
+
+                # Handle RSA key (same as image path)
+                rsa_key_data = None
+                rsa_key_pem = request.form.get("rsa_key_pem", "").strip()
+                rsa_key_qr = request.files.get("rsa_key_qr")
+                rsa_key_from_qr = False
+
+                if rsa_key_pem:
+                    if is_compressed(rsa_key_pem):
+                        rsa_key_pem = decompress_data(rsa_key_pem)
+                    rsa_key_data = rsa_key_pem.encode("utf-8")
+                    rsa_key_from_qr = True
+                elif rsa_key_file and rsa_key_file.filename:
+                    rsa_key_data = rsa_key_file.read()
+                elif rsa_key_qr and rsa_key_qr.filename and HAS_QRCODE_READ:
+                    qr_image_data = rsa_key_qr.read()
+                    key_pem = extract_key_from_qr(qr_image_data)
+                    if key_pem:
+                        rsa_key_data = key_pem.encode("utf-8")
+                        rsa_key_from_qr = True
+                    else:
+                        flash("Could not extract RSA key from QR code image.", "error")
+                        return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                result = validate_security_factors(pin, rsa_key_data)
+                if not result.is_valid:
+                    flash(result.error_message, "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                if pin:
+                    result = validate_pin(pin)
+                    if not result.is_valid:
+                        flash(result.error_message, "error")
+                        return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                key_password = None if rsa_key_from_qr else (rsa_password if rsa_password else None)
+
+                if rsa_key_data:
+                    result = validate_rsa_key(rsa_key_data, key_password)
+                    if not result.is_valid:
+                        flash(result.error_message, "error")
+                        return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                is_async = (
+                    request.form.get("async") == "true" or request.headers.get("X-Async") == "true"
+                )
+
+                decode_params = {
+                    "stego_data": stego_data,
+                    "ref_data": ref_data,
+                    "passphrase": passphrase,
+                    "pin": pin if pin else None,
+                    "rsa_key_data": rsa_key_data,
+                    "rsa_password": key_password,
+                    "embed_mode": embed_mode,
+                    "channel_key": channel_key,
+                }
+
+                if is_async:
+                    job_id = generate_job_id()
+                    _store_job(job_id, {"status": "pending", "created": time.time()})
+                    _executor.submit(_run_decode_audio_job, job_id, decode_params)
+                    return jsonify({"job_id": job_id, "status": "pending"})
+
+                # Sync audio decode
+                decode_result = subprocess_stego.decode_audio(
+                    stego_data=stego_data,
+                    reference_data=ref_data,
+                    passphrase=passphrase,
+                    pin=pin if pin else None,
+                    rsa_key_data=rsa_key_data,
+                    rsa_password=key_password,
+                    embed_mode=embed_mode,
+                    channel_key=channel_key,
+                )
+
+                if not decode_result.success:
+                    error_msg = decode_result.error or "Audio decoding failed"
+                    if (
+                        "decrypt" in error_msg.lower()
+                        or decode_result.error_type == "DecryptionError"
+                    ):
+                        flash(
+                            "Wrong credentials. Double-check your reference photo, "
+                            "passphrase, PIN, and channel key.",
+                            "warning",
+                        )
+                    else:
+                        flash(error_msg, "error")
+                    return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
+
+                if decode_result.is_file:
+                    file_id = secrets.token_urlsafe(16)
+                    cleanup_temp_files()
+                    filename = decode_result.filename or "decoded_file"
+                    temp_storage.save_temp_file(
+                        file_id,
+                        decode_result.file_data,
+                        {
+                            "filename": filename,
+                            "mime_type": decode_result.mime_type,
+                        },
+                    )
+                    return render_template(
+                        "decode.html",
+                        decoded_file=True,
+                        file_id=file_id,
+                        filename=filename,
+                        file_size=format_size(len(decode_result.file_data)),
+                        mime_type=decode_result.mime_type,
+                        has_qrcode_read=HAS_QRCODE_READ,
+                    )
+                else:
+                    return render_template(
+                        "decode.html",
+                        decoded_message=decode_result.message,
+                        has_qrcode_read=HAS_QRCODE_READ,
+                    )
+
+            # ========== IMAGE DECODE PATH (original) ==========
             if not ref_photo or not stego_image:
                 flash("Both reference photo and stego image are required", "error")
                 return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
@@ -1690,7 +2262,9 @@ def decode_page():
                     return render_template("decode.html", has_qrcode_read=HAS_QRCODE_READ)
 
             # Check for async mode (v4.1.5)
-            is_async = request.form.get("async") == "true" or request.headers.get("X-Async") == "true"
+            is_async = (
+                request.form.get("async") == "true" or request.headers.get("X-Async") == "true"
+            )
 
             # Build decode params
             decode_params = {
@@ -1742,10 +2316,14 @@ def decode_page():
                 cleanup_temp_files()
 
                 filename = decode_result.filename or "decoded_file"
-                temp_storage.save_temp_file(file_id, decode_result.file_data, {
-                    "filename": filename,
-                    "mime_type": decode_result.mime_type,
-                })
+                temp_storage.save_temp_file(
+                    file_id,
+                    decode_result.file_data,
+                    {
+                        "filename": filename,
+                        "mime_type": decode_result.mime_type,
+                    },
+                )
 
                 return render_template(
                     "decode.html",
@@ -2101,11 +2679,12 @@ def api_tools_exif_clear():
 @login_required
 def api_tools_rotate():
     """Rotate and/or flip an image, using lossless jpegtran for JPEGs."""
-    from PIL import Image
     import shutil
     import subprocess
     import tempfile
 
+    from PIL import Image
+
     image_file = request.files.get("image")
     if not image_file:
         return jsonify({"success": False, "error": "No image provided"}), 400
@@ -2136,9 +2715,18 @@ def api_tools_rotate():
                 output_path = tempfile.mktemp(suffix=".jpg")
                 try:
                     result = subprocess.run(
-                        ["jpegtran", "-rotate", str(rotation), "-copy", "all",
-                         "-outfile", output_path, input_path],
-                        capture_output=True, timeout=30
+                        [
+                            "jpegtran",
+                            "-rotate",
+                            str(rotation),
+                            "-copy",
+                            "all",
+                            "-outfile",
+                            output_path,
+                            input_path,
+                        ],
+                        capture_output=True,
+                        timeout=30,
                     )
                     if result.returncode == 0:
                         with open(output_path, "rb") as f:
@@ -2158,9 +2746,18 @@ def api_tools_rotate():
                 output_path = tempfile.mktemp(suffix=".jpg")
                 try:
                     result = subprocess.run(
-                        ["jpegtran", "-flip", "horizontal", "-copy", "all",
-                         "-outfile", output_path, input_path],
-                        capture_output=True, timeout=30
+                        [
+                            "jpegtran",
+                            "-flip",
+                            "horizontal",
+                            "-copy",
+                            "all",
+                            "-outfile",
+                            output_path,
+                            input_path,
+                        ],
+                        capture_output=True,
+                        timeout=30,
                     )
                     if result.returncode == 0:
                         with open(output_path, "rb") as f:
@@ -2180,9 +2777,18 @@ def api_tools_rotate():
                 output_path = tempfile.mktemp(suffix=".jpg")
                 try:
                     result = subprocess.run(
-                        ["jpegtran", "-flip", "vertical", "-copy", "all",
-                         "-outfile", output_path, input_path],
-                        capture_output=True, timeout=30
+                        [
+                            "jpegtran",
+                            "-flip",
+                            "vertical",
+                            "-copy",
+                            "all",
+                            "-outfile",
+                            output_path,
+                            input_path,
+                        ],
+                        capture_output=True,
+                        timeout=30,
                     )
                     if result.returncode == 0:
                         with open(output_path, "rb") as f:
@@ -2839,10 +3445,7 @@ def admin_settings_unlock():
     channel_status = get_channel_status()
     channel_key = channel_status.get("key") if channel_status["configured"] else ""
 
-    return jsonify({
-        "success": True,
-        "channel_key": channel_key
-    })
+    return jsonify({"success": True, "channel_key": channel_key})
 
 
 @app.route("/admin/users")
@@ -2976,6 +3579,7 @@ if __name__ == "__main__":
     ssl_context = None
     if app.config.get("HTTPS_ENABLED", False):
         import socket
+
         hostname = os.environ.get("STEGASOO_HOSTNAME") or socket.gethostname()
         try:
             cert_path, key_path = ensure_certs(base_dir, hostname)

frontends/web/auth.py

@@ -77,14 +77,10 @@ def init_db():
     db = get_db()
 
     # Check if we need to migrate from old single-user schema
-    cursor = db.execute(
-        "SELECT name FROM sqlite_master WHERE type='table' AND name='admin_user'"
-    )
+    cursor = db.execute("SELECT name FROM sqlite_master WHERE type='table' AND name='admin_user'")
     has_old_table = cursor.fetchone() is not None
 
-    cursor = db.execute(
-        "SELECT name FROM sqlite_master WHERE type='table' AND name='users'"
-    )
+    cursor = db.execute("SELECT name FROM sqlite_master WHERE type='table' AND name='users'")
     has_new_table = cursor.fetchone() is not None
 
     if has_old_table and not has_new_table:
@@ -189,9 +185,7 @@ def _ensure_channel_keys_table(db: sqlite3.Connection):
 
 def _ensure_app_settings_table(db: sqlite3.Connection):
     """Ensure app_settings table exists (v4.1.0 migration)."""
-    cursor = db.execute(
-        "SELECT name FROM sqlite_master WHERE type='table' AND name='app_settings'"
-    )
+    cursor = db.execute("SELECT name FROM sqlite_master WHERE type='table' AND name='app_settings'")
     if cursor.fetchone() is None:
         db.executescript("""
             CREATE TABLE IF NOT EXISTS app_settings (
@@ -212,9 +206,7 @@ def _ensure_app_settings_table(db: sqlite3.Connection):
 def get_app_setting(key: str) -> str | None:
     """Get an app-level setting value."""
     db = get_db()
-    row = db.execute(
-        "SELECT value FROM app_settings WHERE key = ?", (key,)
-    ).fetchone()
+    row = db.execute("SELECT value FROM app_settings WHERE key = ?", (key,)).fetchone()
     return row["value"] if row else None
 
 
@@ -384,12 +376,10 @@ def get_user_by_username(username: str) -> User | None:
 def get_all_users() -> list[User]:
     """Get all users, admins first, then by creation date."""
     db = get_db()
-    rows = db.execute(
-        """
+    rows = db.execute("""
         SELECT id, username, role, created_at FROM users
         ORDER BY role = 'admin' DESC, created_at ASC
-        """
-    ).fetchall()
+        """).fetchall()
     return [
         User(
             id=row["id"],
@@ -596,9 +586,7 @@ def create_admin_user(username: str, password: str) -> tuple[bool, str]:
     return success, msg
 
 
-def change_password(
-    user_id: int, current_password: str, new_password: str
-) -> tuple[bool, str]:
+def change_password(user_id: int, current_password: str, new_password: str) -> tuple[bool, str]:
     """Change a user's password (requires current password)."""
     user = get_user_by_id(user_id)
     if not user:
@@ -667,9 +655,7 @@ def delete_user(user_id: int, current_user_id: int) -> tuple[bool, str]:
     # Check if this is the last admin
     if user.role == ROLE_ADMIN:
         db = get_db()
-        admin_count = db.execute(
-            "SELECT COUNT(*) FROM users WHERE role = 'admin'"
-        ).fetchone()[0]
+        admin_count = db.execute("SELECT COUNT(*) FROM users WHERE role = 'admin'").fetchone()[0]
         if admin_count <= 1:
             return False, "Cannot delete the last admin"
 
@@ -848,9 +834,7 @@ def save_channel_key(
         return False, "This channel key is already saved", None
 
 
-def update_channel_key_name(
-    key_id: int, user_id: int, new_name: str
-) -> tuple[bool, str]:
+def update_channel_key_name(key_id: int, user_id: int, new_name: str) -> tuple[bool, str]:
     """Update the name of a saved channel key."""
     new_name = new_name.strip()
     if not new_name:

frontends/web/ssl_utils.py

@@ -81,10 +81,12 @@ def generate_self_signed_cert(
     )
 
     # Create certificate
-    subject = issuer = x509.Name([
-        x509.NameAttribute(NameOID.ORGANIZATION_NAME, "Stegasoo"),
-        x509.NameAttribute(NameOID.COMMON_NAME, hostname),
-    ])
+    subject = issuer = x509.Name(
+        [
+            x509.NameAttribute(NameOID.ORGANIZATION_NAME, "Stegasoo"),
+            x509.NameAttribute(NameOID.COMMON_NAME, hostname),
+        ]
+    )
 
     # Subject Alternative Names
     san_list = [
@@ -112,7 +114,7 @@ def generate_self_signed_cert(
         except (ipaddress.AddressValueError, ValueError):
             pass
 
-    now = datetime.datetime.now(datetime.timezone.utc)
+    now = datetime.datetime.now(datetime.UTC)
     cert = (
         x509.CertificateBuilder()
         .subject_name(subject)

frontends/web/static/js/stegasoo.js

@@ -95,7 +95,16 @@ const Stegasoo = {
             if (!isPayloadZone && !isQrZone) {
                 input.addEventListener('change', function() {
                     if (this.files && this.files[0]) {
-                        Stegasoo.showImagePreview(this.files[0], preview, label, zone);
+                        const file = this.files[0];
+                        if (file.type.startsWith('image/') && preview) {
+                            Stegasoo.showImagePreview(file, preview, label, zone);
+                        } else if (file.type.startsWith('audio/') || !file.type.startsWith('image/')) {
+                            // Audio or non-image files: show file info instead of image preview
+                            Stegasoo.showAudioFileInfo(file, zone);
+                            if (label) {
+                                label.classList.add('d-none');
+                            }
+                        }
                     }
                 });
             }
@@ -153,7 +162,21 @@ const Stegasoo = {
         };
         reader.readAsDataURL(file);
     },
-    
+
+    /**
+     * Format audio file info for display in drop zones (v4.3.0)
+     */
+    showAudioFileInfo(file, zone) {
+        const filenameEl = zone.querySelector('.pixel-data-filename span, .scan-data-filename span');
+        const sizeEl = zone.querySelector('.pixel-data-value, .scan-data-value');
+        if (filenameEl) filenameEl.textContent = file.name;
+        if (sizeEl) {
+            const kb = file.size / 1024;
+            sizeEl.textContent = kb >= 1024 ? (kb / 1024).toFixed(1) + ' MB' : kb.toFixed(1) + ' KB';
+        }
+        zone.classList.add('has-file');
+    },
+
     // ========================================================================
     // REFERENCE PHOTO SCAN ANIMATION
     // ========================================================================
@@ -1036,6 +1059,10 @@ const Stegasoo = {
             'saving': 'Saving image...',
             'finalizing': 'Finalizing...',
             'complete': 'Complete!',
+            // Audio encode phases (v4.3.0)
+            'audio_transcoding': 'Transcoding audio...',
+            'audio_embedding': 'Embedding in audio...',
+            'spread_embedding': 'Spread spectrum embedding...',
         };
         return phases[phase] || phase;
     },
@@ -1252,6 +1279,10 @@ const Stegasoo = {
             'verifying': 'Verifying...',
             'finalizing': 'Finalizing...',
             'complete': 'Complete!',
+            // Audio decode phases (v4.3.0)
+            'audio_transcoding': 'Transcoding audio...',
+            'audio_extracting': 'Extracting from audio...',
+            'spread_extracting': 'Spread spectrum extracting...',
         };
         return phases[phase] || phase;
     },

frontends/web/stego_worker.py

@@ -19,6 +19,8 @@ Usage:
 
 import base64
 import json
+import logging
+import os
 import sys
 import traceback
 from pathlib import Path
@@ -27,6 +29,24 @@ from pathlib import Path
 sys.path.insert(0, str(Path(__file__).parent.parent.parent / "src"))
 sys.path.insert(0, str(Path(__file__).parent))
 
+# Configure logging for worker subprocess
+_log_level = os.environ.get("STEGASOO_LOG_LEVEL", "").strip().upper()
+if _log_level and hasattr(logging, _log_level):
+    logging.basicConfig(
+        level=getattr(logging, _log_level),
+        format="[%(asctime)s.%(msecs)03d] [%(levelname)s] [%(name)s] %(message)s",
+        datefmt="%H:%M:%S",
+        stream=sys.stderr,
+    )
+elif os.environ.get("STEGASOO_DEBUG", "").strip() in ("1", "true", "yes"):
+    logging.basicConfig(
+        level=logging.DEBUG,
+        format="[%(asctime)s.%(msecs)03d] [%(levelname)s] [%(name)s] %(message)s",
+        datefmt="%H:%M:%S",
+        stream=sys.stderr,
+    )
+logger = logging.getLogger("stegasoo.worker")
+
 
 def _resolve_channel_key(channel_key_param):
     """
@@ -73,6 +93,7 @@ def _get_channel_info(resolved_key):
 
 def encode_operation(params: dict) -> dict:
     """Handle encode operation."""
+    logger.debug("encode_operation: mode=%s", params.get("embed_mode", "lsb"))
     from stegasoo import FilePayload, encode
 
     # Decode base64 inputs
@@ -142,6 +163,7 @@ def _write_decode_progress(progress_file: str | None, percent: int, phase: str)
         return
     try:
         import json
+
         with open(progress_file, "w") as f:
             json.dump({"percent": percent, "phase": phase}, f)
     except Exception:
@@ -150,6 +172,7 @@ def _write_decode_progress(progress_file: str | None, percent: int, phase: str)
 
 def decode_operation(params: dict) -> dict:
     """Handle decode operation."""
+    logger.debug("decode_operation: mode=%s", params.get("embed_mode", "auto"))
     from stegasoo import decode
 
     progress_file = params.get("progress_file")
@@ -233,6 +256,145 @@ def capacity_check_operation(params: dict) -> dict:
     }
 
 
+def encode_audio_operation(params: dict) -> dict:
+    """Handle audio encode operation (v4.3.0)."""
+    logger.debug("encode_audio_operation: mode=%s", params.get("embed_mode", "audio_lsb"))
+    from stegasoo import FilePayload, encode_audio
+
+    carrier_data = base64.b64decode(params["carrier_b64"])
+    reference_data = base64.b64decode(params["reference_b64"])
+
+    # Optional RSA key
+    rsa_key_data = None
+    if params.get("rsa_key_b64"):
+        rsa_key_data = base64.b64decode(params["rsa_key_b64"])
+
+    # Determine payload type
+    if params.get("file_b64"):
+        file_data = base64.b64decode(params["file_b64"])
+        payload = FilePayload(
+            data=file_data,
+            filename=params.get("file_name", "file"),
+            mime_type=params.get("file_mime", "application/octet-stream"),
+        )
+    else:
+        payload = params.get("message", "")
+
+    resolved_channel_key = _resolve_channel_key(params.get("channel_key", "auto"))
+
+    # Resolve chip_tier from params (None means use default)
+    chip_tier_val = params.get("chip_tier")
+    if chip_tier_val is not None:
+        chip_tier_val = int(chip_tier_val)
+
+    stego_audio, stats = encode_audio(
+        message=payload,
+        reference_photo=reference_data,
+        carrier_audio=carrier_data,
+        passphrase=params.get("passphrase", ""),
+        pin=params.get("pin"),
+        rsa_key_data=rsa_key_data,
+        rsa_password=params.get("rsa_password"),
+        embed_mode=params.get("embed_mode", "audio_lsb"),
+        channel_key=resolved_channel_key,
+        progress_file=params.get("progress_file"),
+        chip_tier=chip_tier_val,
+    )
+
+    channel_mode, channel_fingerprint = _get_channel_info(resolved_channel_key)
+
+    return {
+        "success": True,
+        "stego_b64": base64.b64encode(stego_audio).decode("ascii"),
+        "stats": {
+            "samples_modified": stats.samples_modified,
+            "total_samples": stats.total_samples,
+            "capacity_used": stats.capacity_used,
+            "bytes_embedded": stats.bytes_embedded,
+            "sample_rate": stats.sample_rate,
+            "channels": stats.channels,
+            "duration_seconds": stats.duration_seconds,
+            "embed_mode": stats.embed_mode,
+        },
+        "channel_mode": channel_mode,
+        "channel_fingerprint": channel_fingerprint,
+    }
+
+
+def decode_audio_operation(params: dict) -> dict:
+    """Handle audio decode operation (v4.3.0)."""
+    logger.debug("decode_audio_operation: mode=%s", params.get("embed_mode", "audio_auto"))
+    from stegasoo import decode_audio
+
+    progress_file = params.get("progress_file")
+    _write_decode_progress(progress_file, 5, "reading")
+
+    stego_data = base64.b64decode(params["stego_b64"])
+    reference_data = base64.b64decode(params["reference_b64"])
+
+    _write_decode_progress(progress_file, 15, "reading")
+
+    rsa_key_data = None
+    if params.get("rsa_key_b64"):
+        rsa_key_data = base64.b64decode(params["rsa_key_b64"])
+
+    resolved_channel_key = _resolve_channel_key(params.get("channel_key", "auto"))
+
+    result = decode_audio(
+        stego_audio=stego_data,
+        reference_photo=reference_data,
+        passphrase=params.get("passphrase", ""),
+        pin=params.get("pin"),
+        rsa_key_data=rsa_key_data,
+        rsa_password=params.get("rsa_password"),
+        embed_mode=params.get("embed_mode", "audio_auto"),
+        channel_key=resolved_channel_key,
+        progress_file=progress_file,
+    )
+
+    if result.is_file:
+        return {
+            "success": True,
+            "is_file": True,
+            "file_b64": base64.b64encode(result.file_data).decode("ascii"),
+            "filename": result.filename,
+            "mime_type": result.mime_type,
+        }
+    else:
+        return {
+            "success": True,
+            "is_file": False,
+            "message": result.message,
+        }
+
+
+def audio_info_operation(params: dict) -> dict:
+    """Handle audio info operation (v4.3.0)."""
+    from stegasoo import get_audio_info
+    from stegasoo.audio_steganography import calculate_audio_lsb_capacity
+    from stegasoo.spread_steganography import calculate_audio_spread_capacity
+
+    audio_data = base64.b64decode(params["audio_b64"])
+
+    info = get_audio_info(audio_data)
+    lsb_capacity = calculate_audio_lsb_capacity(audio_data)
+    spread_capacity = calculate_audio_spread_capacity(audio_data)
+
+    return {
+        "success": True,
+        "info": {
+            "sample_rate": info.sample_rate,
+            "channels": info.channels,
+            "duration_seconds": round(info.duration_seconds, 2),
+            "num_samples": info.num_samples,
+            "format": info.format,
+            "bit_depth": info.bit_depth,
+            "capacity_lsb": lsb_capacity,
+            "capacity_spread": spread_capacity.usable_capacity_bytes,
+        },
+    }
+
+
 def channel_status_operation(params: dict) -> dict:
     """Handle channel status check (v4.0.0)."""
     from stegasoo import get_channel_status
@@ -263,6 +425,7 @@ def main():
         else:
             params = json.loads(input_text)
             operation = params.get("operation")
+            logger.info("Worker handling operation: %s", operation)
 
             if operation == "encode":
                 output = encode_operation(params)
@@ -274,6 +437,13 @@ def main():
                 output = capacity_check_operation(params)
             elif operation == "channel_status":
                 output = channel_status_operation(params)
+            # Audio operations (v4.3.0)
+            elif operation == "encode_audio":
+                output = encode_audio_operation(params)
+            elif operation == "decode_audio":
+                output = decode_audio_operation(params)
+            elif operation == "audio_info":
+                output = audio_info_operation(params)
             else:
                 output = {"success": False, "error": f"Unknown operation: {operation}"}
 

frontends/web/subprocess_stego.py

@@ -115,6 +115,35 @@ class CapacityResult:
     error: str | None = None
 
 
+@dataclass
+class AudioEncodeResult:
+    """Result from audio encode operation (v4.3.0)."""
+
+    success: bool
+    stego_data: bytes | None = None
+    stats: dict[str, Any] | None = None
+    channel_mode: str | None = None
+    channel_fingerprint: str | None = None
+    error: str | None = None
+    error_type: str | None = None
+
+
+@dataclass
+class AudioInfoResult:
+    """Result from audio info operation (v4.3.0)."""
+
+    success: bool
+    sample_rate: int = 0
+    channels: int = 0
+    duration_seconds: float = 0.0
+    num_samples: int = 0
+    format: str = ""
+    bit_depth: int | None = None
+    capacity_lsb: int = 0
+    capacity_spread: int = 0
+    error: str | None = None
+
+
 @dataclass
 class ChannelStatusResult:
     """Result from channel status check (v4.0.0)."""
@@ -456,6 +485,201 @@ class SubprocessStego:
                 error=result.get("error", "Unknown error"),
             )
 
+    # =========================================================================
+    # Audio Steganography (v4.3.0)
+    # =========================================================================
+
+    def encode_audio(
+        self,
+        carrier_data: bytes,
+        reference_data: bytes,
+        message: str | None = None,
+        file_data: bytes | None = None,
+        file_name: str | None = None,
+        file_mime: str | None = None,
+        passphrase: str = "",
+        pin: str | None = None,
+        rsa_key_data: bytes | None = None,
+        rsa_password: str | None = None,
+        embed_mode: str = "audio_lsb",
+        channel_key: str | None = "auto",
+        timeout: int | None = None,
+        progress_file: str | None = None,
+        chip_tier: int | None = None,
+    ) -> AudioEncodeResult:
+        """
+        Encode a message or file into an audio carrier.
+
+        Args:
+            carrier_data: Carrier audio bytes (WAV, FLAC, MP3, etc.)
+            reference_data: Reference photo bytes
+            message: Text message to encode (if not file)
+            file_data: File bytes to encode (if not message)
+            file_name: Original filename (for file payload)
+            file_mime: MIME type (for file payload)
+            passphrase: Encryption passphrase
+            pin: Optional PIN
+            rsa_key_data: Optional RSA key PEM bytes
+            rsa_password: RSA key password if encrypted
+            embed_mode: 'audio_lsb' or 'audio_spread'
+            channel_key: 'auto', 'none', or explicit key
+            timeout: Operation timeout (default 300s for audio)
+            progress_file: Path to write progress updates
+
+        Returns:
+            AudioEncodeResult with stego audio data on success
+        """
+        params = {
+            "operation": "encode_audio",
+            "carrier_b64": base64.b64encode(carrier_data).decode("ascii"),
+            "reference_b64": base64.b64encode(reference_data).decode("ascii"),
+            "message": message,
+            "passphrase": passphrase,
+            "pin": pin,
+            "embed_mode": embed_mode,
+            "channel_key": channel_key,
+            "progress_file": progress_file,
+            "chip_tier": chip_tier,
+        }
+
+        if file_data:
+            params["file_b64"] = base64.b64encode(file_data).decode("ascii")
+            params["file_name"] = file_name
+            params["file_mime"] = file_mime
+
+        if rsa_key_data:
+            params["rsa_key_b64"] = base64.b64encode(rsa_key_data).decode("ascii")
+            params["rsa_password"] = rsa_password
+
+        # Audio operations can be slower (especially spread spectrum)
+        result = self._run_worker(params, timeout or 300)
+
+        if result.get("success"):
+            return AudioEncodeResult(
+                success=True,
+                stego_data=base64.b64decode(result["stego_b64"]),
+                stats=result.get("stats"),
+                channel_mode=result.get("channel_mode"),
+                channel_fingerprint=result.get("channel_fingerprint"),
+            )
+        else:
+            return AudioEncodeResult(
+                success=False,
+                error=result.get("error", "Unknown error"),
+                error_type=result.get("error_type"),
+            )
+
+    def decode_audio(
+        self,
+        stego_data: bytes,
+        reference_data: bytes,
+        passphrase: str = "",
+        pin: str | None = None,
+        rsa_key_data: bytes | None = None,
+        rsa_password: str | None = None,
+        embed_mode: str = "audio_auto",
+        channel_key: str | None = "auto",
+        timeout: int | None = None,
+        progress_file: str | None = None,
+    ) -> DecodeResult:
+        """
+        Decode a message or file from stego audio.
+
+        Args:
+            stego_data: Stego audio bytes
+            reference_data: Reference photo bytes
+            passphrase: Decryption passphrase
+            pin: Optional PIN
+            rsa_key_data: Optional RSA key PEM bytes
+            rsa_password: RSA key password if encrypted
+            embed_mode: 'audio_auto', 'audio_lsb', or 'audio_spread'
+            channel_key: 'auto', 'none', or explicit key
+            timeout: Operation timeout (default 300s for audio)
+            progress_file: Path to write progress updates
+
+        Returns:
+            DecodeResult with message or file_data on success
+        """
+        params = {
+            "operation": "decode_audio",
+            "stego_b64": base64.b64encode(stego_data).decode("ascii"),
+            "reference_b64": base64.b64encode(reference_data).decode("ascii"),
+            "passphrase": passphrase,
+            "pin": pin,
+            "embed_mode": embed_mode,
+            "channel_key": channel_key,
+            "progress_file": progress_file,
+        }
+
+        if rsa_key_data:
+            params["rsa_key_b64"] = base64.b64encode(rsa_key_data).decode("ascii")
+            params["rsa_password"] = rsa_password
+
+        result = self._run_worker(params, timeout or 300)
+
+        if result.get("success"):
+            if result.get("is_file"):
+                return DecodeResult(
+                    success=True,
+                    is_file=True,
+                    file_data=base64.b64decode(result["file_b64"]),
+                    filename=result.get("filename"),
+                    mime_type=result.get("mime_type"),
+                )
+            else:
+                return DecodeResult(
+                    success=True,
+                    is_file=False,
+                    message=result.get("message"),
+                )
+        else:
+            return DecodeResult(
+                success=False,
+                error=result.get("error", "Unknown error"),
+                error_type=result.get("error_type"),
+            )
+
+    def audio_info(
+        self,
+        audio_data: bytes,
+        timeout: int | None = None,
+    ) -> AudioInfoResult:
+        """
+        Get audio file information and steganographic capacity.
+
+        Args:
+            audio_data: Audio file bytes
+            timeout: Operation timeout in seconds
+
+        Returns:
+            AudioInfoResult with metadata and capacity info
+        """
+        params = {
+            "operation": "audio_info",
+            "audio_b64": base64.b64encode(audio_data).decode("ascii"),
+        }
+
+        result = self._run_worker(params, timeout)
+
+        if result.get("success"):
+            info = result.get("info", {})
+            return AudioInfoResult(
+                success=True,
+                sample_rate=info.get("sample_rate", 0),
+                channels=info.get("channels", 0),
+                duration_seconds=info.get("duration_seconds", 0.0),
+                num_samples=info.get("num_samples", 0),
+                format=info.get("format", ""),
+                bit_depth=info.get("bit_depth"),
+                capacity_lsb=info.get("capacity_lsb", 0),
+                capacity_spread=info.get("capacity_spread", 0),
+            )
+        else:
+            return AudioInfoResult(
+                success=False,
+                error=result.get("error", "Unknown error"),
+            )
+
     def get_channel_status(
         self,
         reveal: bool = False,

frontends/web/templates/decode.html

@@ -24,7 +24,11 @@
     border-left: 3px solid #ffe699;
 }
 .step-accordion .accordion-button::after {
-    filter: invert(1) sepia(1) saturate(2) hue-rotate(5deg) brightness(1.2);
+    filter: brightness(0) invert(1);
+    opacity: 0.5;
+}
+.step-accordion .accordion-button:not(.collapsed)::after {
+    opacity: 0.9;
 }
 .step-accordion .accordion-body {
     background: rgba(30, 40, 50, 0.4);
@@ -172,19 +176,51 @@
                     <div class="accordion step-accordion" id="decodeAccordion">
 
                         <!-- ================================================================
-                             STEP 1: IMAGES & MODE
+                             STEP 1: CARRIER TYPE (v4.3.0)
+                             ================================================================ -->
+                        <div class="accordion-item" id="carrierTypeStep">
+                            <h2 class="accordion-header">
+                                <button class="accordion-button" type="button" data-bs-toggle="collapse" data-bs-target="#stepCarrierType">
+                                    <span class="step-title">
+                                        <span class="step-number" id="stepCarrierTypeNumber">1</span>
+                                        <i class="bi bi-collection me-1"></i> Carrier Type
+                                    </span>
+                                    <span class="step-summary" id="stepCarrierTypeSummary"></span>
+                                </button>
+                            </h2>
+                            <div id="stepCarrierType" class="accordion-collapse collapse show" data-bs-parent="#decodeAccordion">
+                                <div class="accordion-body">
+                                    <input type="hidden" name="carrier_type" id="carrierTypeInput" value="image">
+                                    <div class="btn-group w-100" role="group">
+                                        <input type="radio" class="btn-check" name="carrier_type_select" id="typeImage" value="image" checked>
+                                        <label class="btn btn-outline-secondary" for="typeImage">
+                                            <i class="bi bi-image me-1"></i> Image
+                                        </label>
+                                        <input type="radio" class="btn-check" name="carrier_type_select" id="typeAudio" value="audio"
+                                               {% if not has_audio %}disabled{% endif %}>
+                                        <label class="btn btn-outline-secondary {% if not has_audio %}disabled text-muted{% endif %}" for="typeAudio">
+                                            <i class="bi bi-music-note-beamed me-1"></i> Audio
+                                            {% if not has_audio %}<small class="d-block" style="font-size: 0.65rem;">(not available)</small>{% endif %}
+                                        </label>
+                                    </div>
+                                </div>
+                            </div>
+                        </div>
+
+                        <!-- ================================================================
+                             STEP 2: IMAGES & MODE
                              ================================================================ -->
                         <div class="accordion-item">
                             <h2 class="accordion-header">
-                                <button class="accordion-button" type="button" data-bs-toggle="collapse" data-bs-target="#stepImages">
+                                <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#stepImages">
                                     <span class="step-title">
-                                        <span class="step-number" id="stepImagesNumber">1</span>
-                                        <i class="bi bi-images me-1"></i> Images & Mode
+                                        <span class="step-number" id="stepImagesNumber">2</span>
+                                        <i class="bi bi-images me-1"></i> Reference, Carrier, Mode
                                     </span>
                                     <span class="step-summary" id="stepImagesSummary">Select reference & stego</span>
                                 </button>
                             </h2>
-                            <div id="stepImages" class="accordion-collapse collapse show" data-bs-parent="#decodeAccordion">
+                            <div id="stepImages" class="accordion-collapse collapse" data-bs-parent="#decodeAccordion">
                                 <div class="accordion-body">
 
                                     <div class="row">
@@ -213,41 +249,74 @@
                                         </div>
 
                                         <div class="col-md-6 mb-3">
-                                            <label class="form-label">
-                                                <i class="bi bi-file-earmark-image me-1"></i> Stego Image
-                                            </label>
-                                            <div class="drop-zone pixel-container" id="stegoDropZone">
-                                                <input type="file" name="stego_image" accept="image/*" required id="stegoInput">
-                                                <div class="drop-zone-label">
-                                                    <i class="bi bi-cloud-arrow-up fs-3 d-block mb-2 text-muted"></i>
-                                                    <span class="text-muted">Drop image or click</span>
-                                                </div>
-                                                <img class="drop-zone-preview d-none" id="stegoPreview">
-                                                <div class="pixel-blocks"></div>
-                                                <div class="pixel-scan-line"></div>
-                                                <div class="pixel-corners">
-                                                    <div class="pixel-corner tl"></div><div class="pixel-corner tr"></div>
-                                                    <div class="pixel-corner bl"></div><div class="pixel-corner br"></div>
-                                                </div>
-                                                <div class="pixel-data-panel">
-                                                    <div class="pixel-data-filename"><i class="bi bi-check-circle-fill"></i><span id="stegoFileName">image.png</span></div>
-                                                    <div class="pixel-data-row"><span class="pixel-status-badge">Stego Loaded</span><span class="pixel-data-value" id="stegoFileSize">--</span></div>
-                                                    <div class="pixel-dimensions" id="stegoDims">-- x -- px</div>
+                                            <div id="imageStegoSection">
+                                                <label class="form-label">
+                                                    <i class="bi bi-file-earmark-image me-1"></i> Stego Image
+                                                </label>
+                                                <div class="drop-zone pixel-container" id="stegoDropZone">
+                                                    <input type="file" name="stego_image" accept="image/*" required id="stegoInput">
+                                                    <div class="drop-zone-label">
+                                                        <i class="bi bi-cloud-arrow-up fs-3 d-block mb-2 text-muted"></i>
+                                                        <span class="text-muted">Drop image or click</span>
+                                                    </div>
+                                                    <img class="drop-zone-preview d-none" id="stegoPreview">
+                                                    <div class="pixel-blocks"></div>
+                                                    <div class="pixel-scan-line"></div>
+                                                    <div class="pixel-corners">
+                                                        <div class="pixel-corner tl"></div><div class="pixel-corner tr"></div>
+                                                        <div class="pixel-corner bl"></div><div class="pixel-corner br"></div>
+                                                    </div>
+                                                    <div class="pixel-data-panel">
+                                                        <div class="pixel-data-filename"><i class="bi bi-check-circle-fill"></i><span id="stegoFileName">image.png</span></div>
+                                                        <div class="pixel-data-row"><span class="pixel-status-badge">Stego Loaded</span><span class="pixel-data-value" id="stegoFileSize">--</span></div>
+                                                        <div class="pixel-dimensions" id="stegoDims">-- x -- px</div>
+                                                    </div>
                                                 </div>
+                                                <div class="form-text">Image containing the hidden message</div>
+                                            </div>
+                                            <!-- Audio Stego (hidden by default) -->
+                                            <div class="d-none" id="audioStegoSection">
+                                                <label class="form-label">
+                                                    <i class="bi bi-file-earmark-music me-1"></i> Stego Audio
+                                                </label>
+                                                <div class="drop-zone pixel-container" id="audioStegoDropZone">
+                                                    <input type="file" name="stego_image" accept="audio/*" id="audioStegoInput">
+                                                    <div class="drop-zone-label">
+                                                        <i class="bi bi-music-note-beamed fs-3 d-block mb-2 text-muted"></i>
+                                                        <span class="text-muted">Drop audio or click</span>
+                                                    </div>
+                                                    <div class="pixel-data-panel">
+                                                        <div class="pixel-data-filename"><i class="bi bi-check-circle-fill"></i><span id="audioStegoFileName">audio.wav</span></div>
+                                                        <div class="pixel-data-row"><span class="pixel-status-badge">Audio Loaded</span><span class="pixel-data-value" id="audioStegoFileSize">--</span></div>
+                                                    </div>
+                                                </div>
+                                                <div class="form-text">Audio file containing the hidden message</div>
                                             </div>
-                                            <div class="form-text">Image containing the hidden message</div>
                                         </div>
                                     </div>
 
                                     <!-- Extraction Mode -->
                                     <div class="d-flex gap-2 align-items-center flex-wrap mb-2">
-                                        <div class="btn-group" role="group">
-                                            <input type="radio" class="btn-check" name="embed_mode" id="modeAuto" value="auto" checked>
-                                            <label class="btn btn-outline-secondary text-nowrap" for="modeAuto"><i class="bi bi-magic me-1"></i>Auto</label>
-                                            <input type="radio" class="btn-check" name="embed_mode" id="modeLsb" value="lsb">
-                                            <label class="btn btn-outline-secondary text-nowrap" for="modeLsb"><i class="bi bi-grid-3x3-gap me-1"></i>LSB</label>
-                                            <input type="radio" class="btn-check" name="embed_mode" id="modeDct" value="dct" {% if not has_dct %}disabled{% endif %}>
-                                            <label class="btn btn-outline-secondary text-nowrap" for="modeDct" id="dctModeLabel"><i class="bi bi-soundwave me-1"></i>DCT</label>
+                                        <div id="imageModeGroup">
+                                            <div class="btn-group" role="group">
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeAuto" value="auto" checked>
+                                                <label class="btn btn-outline-secondary text-nowrap" for="modeAuto"><i class="bi bi-magic me-1"></i>Auto</label>
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeLsb" value="lsb">
+                                                <label class="btn btn-outline-secondary text-nowrap" for="modeLsb"><i class="bi bi-grid-3x3-gap me-1"></i>LSB</label>
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeDct" value="dct" {% if not has_dct %}disabled{% endif %}>
+                                                <label class="btn btn-outline-secondary text-nowrap" for="modeDct" id="dctModeLabel"><i class="bi bi-soundwave me-1"></i>DCT</label>
+                                            </div>
+                                        </div>
+                                        <!-- Audio Extraction Modes (hidden by default) -->
+                                        <div class="d-none" id="audioModeGroup">
+                                            <div class="btn-group" role="group">
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeAudioAuto" value="audio_auto">
+                                                <label class="btn btn-outline-secondary text-nowrap" for="modeAudioAuto"><i class="bi bi-magic me-1"></i>Auto</label>
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeAudioLsb" value="audio_lsb">
+                                                <label class="btn btn-outline-secondary text-nowrap" for="modeAudioLsb"><i class="bi bi-grid-3x3-gap me-1"></i>LSB</label>
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeAudioSpread" value="audio_spread">
+                                                <label class="btn btn-outline-secondary text-nowrap" for="modeAudioSpread"><i class="bi bi-broadcast me-1"></i>Spread</label>
+                                            </div>
                                         </div>
                                     </div>
                                     <div class="form-text" id="modeHint">
@@ -259,13 +328,13 @@
                         </div>
 
                         <!-- ================================================================
-                             STEP 2: SECURITY
+                             STEP 3: SECURITY
                              ================================================================ -->
                         <div class="accordion-item">
                             <h2 class="accordion-header">
                                 <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#stepSecurity">
                                     <span class="step-title">
-                                        <span class="step-number" id="stepSecurityNumber">2</span>
+                                        <span class="step-number" id="stepSecurityNumber">3</span>
                                         <i class="bi bi-shield-lock me-1"></i> Security
                                     </span>
                                     <span class="step-summary" id="stepSecuritySummary">Passphrase & keys</span>
@@ -425,7 +494,10 @@
 const modeHints = {
     auto: { icon: 'lightning', text: 'Tries LSB first, then DCT' },
     lsb: { icon: 'hdd', text: 'For email and direct transfers' },
-    dct: { icon: 'phone', text: 'For social media images' }
+    dct: { icon: 'phone', text: 'For social media images' },
+    audio_auto: { icon: 'lightning', text: 'Tries LSB first, then Spread Spectrum' },
+    audio_lsb: { icon: 'grid-3x3-gap', text: 'Direct bit embedding in audio samples' },
+    audio_spread: { icon: 'broadcast', text: 'Noise-resistant spread spectrum encoding' }
 };
 
 document.querySelectorAll('input[name="embed_mode"]').forEach(radio => {
@@ -442,9 +514,14 @@ document.querySelectorAll('input[name="embed_mode"]').forEach(radio => {
 // ACCORDION SUMMARY UPDATES
 // ============================================================================
 
+const carrierTypeInput = document.getElementById('carrierTypeInput');
+
 function updateImagesSummary() {
     const ref = document.getElementById('refPhotoInput')?.files[0];
-    const stego = document.getElementById('stegoInput')?.files[0];
+    const isAudio = carrierTypeInput?.value === 'audio';
+    const stego = isAudio
+        ? document.getElementById('audioStegoInput')?.files[0]
+        : document.getElementById('stegoInput')?.files[0];
     const mode = document.querySelector('input[name="embed_mode"]:checked')?.value?.toUpperCase() || 'AUTO';
     const summary = document.getElementById('stepImagesSummary');
     const stepNum = document.getElementById('stepImagesNumber');
@@ -460,12 +537,12 @@ function updateImagesSummary() {
         summary.textContent = ref ? ref.name.slice(0, 15) : stego.name.slice(0, 15);
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '1';
+        stepNum.textContent = '2';
     } else {
-        summary.textContent = 'Select reference & stego';
+        summary.textContent = isAudio ? 'Select reference & audio' : 'Select reference & stego';
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '1';
+        stepNum.textContent = '2';
     }
 }
 
@@ -493,19 +570,99 @@ function updateSecuritySummary() {
         summary.textContent = 'Passphrase & keys';
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '2';
+        stepNum.textContent = '3';
     }
 }
 
 // Attach listeners
 document.getElementById('refPhotoInput')?.addEventListener('change', updateImagesSummary);
 document.getElementById('stegoInput')?.addEventListener('change', updateImagesSummary);
+document.getElementById('audioStegoInput')?.addEventListener('change', updateImagesSummary);
 document.querySelectorAll('input[name="embed_mode"]').forEach(r => r.addEventListener('change', updateImagesSummary));
+document.querySelectorAll('#audioModeGroup input[name="embed_mode"]').forEach(r => r.addEventListener('change', updateImagesSummary));
 
 document.getElementById('passphraseInput')?.addEventListener('input', updateSecuritySummary);
 document.getElementById('pinInput')?.addEventListener('input', updateSecuritySummary);
 document.querySelector('input[name="rsa_key"]')?.addEventListener('change', updateSecuritySummary);
 
+// ============================================================================
+// CARRIER TYPE TOGGLE (v4.3.0)
+// ============================================================================
+
+const carrierTypeRadios = document.querySelectorAll('input[name="carrier_type_select"]');
+const imageStegoSection = document.getElementById('imageStegoSection');
+const audioStegoSection = document.getElementById('audioStegoSection');
+const imageModeGroup = document.getElementById('imageModeGroup');
+const audioModeGroup = document.getElementById('audioModeGroup');
+const stepCarrierTypeSummary = document.getElementById('stepCarrierTypeSummary');
+
+carrierTypeRadios.forEach(radio => {
+    radio.addEventListener('change', function() {
+        const isAudio = this.value === 'audio';
+        carrierTypeInput.value = this.value;
+
+        // Toggle stego sections
+        if (imageStegoSection) imageStegoSection.classList.toggle('d-none', isAudio);
+        if (audioStegoSection) audioStegoSection.classList.toggle('d-none', !isAudio);
+
+        // Toggle required attribute so hidden inputs don't block form submission
+        const imgStego = document.getElementById('stegoInput');
+        const audStego = document.getElementById('audioStegoInput');
+        if (imgStego) { if (isAudio) imgStego.removeAttribute('required'); else imgStego.setAttribute('required', ''); }
+        if (audStego) { if (isAudio) audStego.setAttribute('required', ''); else audStego.removeAttribute('required'); }
+
+        // Toggle mode groups
+        if (imageModeGroup) imageModeGroup.classList.toggle('d-none', isAudio);
+        if (audioModeGroup) audioModeGroup.classList.toggle('d-none', !isAudio);
+
+        // Update summary
+        if (stepCarrierTypeSummary) {
+            stepCarrierTypeSummary.textContent = isAudio ? 'Audio' : 'Image';
+        }
+
+        // Select default mode
+        if (isAudio) {
+            const audioAuto = document.getElementById('modeAudioAuto');
+            if (audioAuto) audioAuto.checked = true;
+        } else {
+            const autoMode = document.getElementById('modeAuto');
+            if (autoMode) autoMode.checked = true;
+        }
+
+        // Clear stego file selections
+        const stegoInput = document.getElementById('stegoInput');
+        const audioStegoInput = document.getElementById('audioStegoInput');
+        if (stegoInput) stegoInput.value = '';
+        if (audioStegoInput) audioStegoInput.value = '';
+
+        // Reset previews
+        document.getElementById('stegoPreview')?.classList.add('d-none');
+
+        // Update mode hint
+        const hint = document.getElementById('modeHint');
+        if (hint) {
+            if (isAudio) {
+                hint.innerHTML = '<i class="bi bi-lightning me-1"></i>Tries LSB first, then Spread Spectrum';
+            } else {
+                hint.innerHTML = '<i class="bi bi-lightning me-1"></i>Tries LSB first, then DCT';
+            }
+        }
+
+        updateImagesSummary();
+    });
+});
+
+// Audio stego file info display
+const audioStegoInput = document.getElementById('audioStegoInput');
+audioStegoInput?.addEventListener('change', function() {
+    if (this.files && this.files[0]) {
+        const file = this.files[0];
+        document.getElementById('audioStegoFileName').textContent = file.name;
+        document.getElementById('audioStegoFileSize').textContent = (file.size / 1024).toFixed(1) + ' KB';
+        updateImagesSummary();
+    }
+});
+
 // ============================================================================
 // MODE SWITCHING
 // ============================================================================

frontends/web/templates/encode.html

@@ -24,7 +24,11 @@
     border-left: 3px solid #ffe699;
 }
 .step-accordion .accordion-button::after {
-    filter: invert(1) sepia(1) saturate(2) hue-rotate(5deg) brightness(1.2);
+    filter: brightness(0) invert(1);
+    opacity: 0.5;
+}
+.step-accordion .accordion-button:not(.collapsed)::after {
+    opacity: 0.9;
 }
 .step-accordion .accordion-body {
     background: rgba(30, 40, 50, 0.4);
@@ -126,19 +130,56 @@
                     <div class="accordion step-accordion" id="encodeAccordion">
 
                         <!-- ================================================================
-                             STEP 1: IMAGES
+                             STEP 1: CARRIER TYPE (v4.3.0)
+                             ================================================================ -->
+                        <div class="accordion-item" id="carrierTypeStep">
+                            <h2 class="accordion-header">
+                                <button class="accordion-button" type="button" data-bs-toggle="collapse" data-bs-target="#stepCarrierType">
+                                    <span class="step-title">
+                                        <span class="step-number" id="stepCarrierTypeNumber">1</span>
+                                        <i class="bi bi-collection me-1"></i> Carrier Type
+                                    </span>
+                                    <span class="step-summary" id="stepCarrierTypeSummary"></span>
+                                </button>
+                            </h2>
+                            <div id="stepCarrierType" class="accordion-collapse collapse show" data-bs-parent="#encodeAccordion">
+                                <div class="accordion-body">
+                                    <input type="hidden" name="carrier_type" id="carrierTypeInput" value="image">
+                                    <div class="btn-group w-100" role="group">
+                                        <input type="radio" class="btn-check" name="carrier_type_select" id="typeImage" value="image" checked>
+                                        <label class="btn btn-outline-secondary" for="typeImage">
+                                            <i class="bi bi-image me-1"></i> Image
+                                        </label>
+                                        <input type="radio" class="btn-check" name="carrier_type_select" id="typeAudio" value="audio"
+                                               {% if not has_audio %}disabled{% endif %}>
+                                        <label class="btn btn-outline-secondary {% if not has_audio %}disabled text-muted{% endif %}" for="typeAudio">
+                                            <i class="bi bi-music-note-beamed me-1"></i> Audio
+                                            {% if not has_audio %}<small class="d-block" style="font-size: 0.65rem;">(not available)</small>{% endif %}
+                                        </label>
+                                    </div>
+                                    {% if not has_audio %}
+                                    <div class="form-text text-warning mt-2">
+                                        <i class="bi bi-exclamation-triangle me-1"></i>Audio requires numpy and soundfile packages
+                                    </div>
+                                    {% endif %}
+                                </div>
+                            </div>
+                        </div>
+
+                        <!-- ================================================================
+                             STEP 2: IMAGES & MODE
                              ================================================================ -->
                         <div class="accordion-item">
                             <h2 class="accordion-header">
-                                <button class="accordion-button" type="button" data-bs-toggle="collapse" data-bs-target="#stepImages">
+                                <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#stepImages">
                                     <span class="step-title">
-                                        <span class="step-number" id="stepImagesNumber">1</span>
-                                        <i class="bi bi-images me-1"></i> Images & Mode
+                                        <span class="step-number" id="stepImagesNumber">2</span>
+                                        <i class="bi bi-images me-1"></i> Reference, Carrier, Mode
                                     </span>
                                     <span class="step-summary" id="stepImagesSummary">Select reference & carrier</span>
                                 </button>
                             </h2>
-                            <div id="stepImages" class="accordion-collapse collapse show" data-bs-parent="#encodeAccordion">
+                            <div id="stepImages" class="accordion-collapse collapse" data-bs-parent="#encodeAccordion">
                                 <div class="accordion-body">
 
                                     <div class="row">
@@ -167,29 +208,51 @@
                                         </div>
 
                                         <div class="col-md-6 mb-3">
-                                            <label class="form-label">
-                                                <i class="bi bi-file-earmark-image me-1"></i> Carrier Image
-                                            </label>
-                                            <div class="drop-zone pixel-container" id="carrierDropZone">
-                                                <input type="file" name="carrier" accept="image/*" required id="carrierInput">
-                                                <div class="drop-zone-label">
-                                                    <i class="bi bi-cloud-arrow-up fs-3 d-block mb-2 text-muted"></i>
-                                                    <span class="text-muted">Drop image or click</span>
-                                                </div>
-                                                <img class="drop-zone-preview d-none" id="carrierPreview">
-                                                <div class="pixel-blocks"></div>
-                                                <div class="pixel-scan-line"></div>
-                                                <div class="pixel-corners">
-                                                    <div class="pixel-corner tl"></div><div class="pixel-corner tr"></div>
-                                                    <div class="pixel-corner bl"></div><div class="pixel-corner br"></div>
-                                                </div>
-                                                <div class="pixel-data-panel">
-                                                    <div class="pixel-data-filename"><i class="bi bi-check-circle-fill"></i><span id="carrierFileName">image.jpg</span></div>
-                                                    <div class="pixel-data-row"><span class="pixel-status-badge">Carrier Loaded</span><span class="pixel-data-value" id="carrierFileSize">--</span></div>
-                                                    <div class="pixel-dimensions" id="carrierDims">-- x -- px</div>
+                                            <div id="imageCarrierSection">
+                                                <label class="form-label">
+                                                    <i class="bi bi-file-earmark-image me-1"></i> Carrier Image
+                                                </label>
+                                                <div class="drop-zone pixel-container" id="carrierDropZone">
+                                                    <input type="file" name="carrier" accept="image/*" required id="carrierInput">
+                                                    <div class="drop-zone-label">
+                                                        <i class="bi bi-cloud-arrow-up fs-3 d-block mb-2 text-muted"></i>
+                                                        <span class="text-muted">Drop image or click</span>
+                                                    </div>
+                                                    <img class="drop-zone-preview d-none" id="carrierPreview">
+                                                    <div class="pixel-blocks"></div>
+                                                    <div class="pixel-scan-line"></div>
+                                                    <div class="pixel-corners">
+                                                        <div class="pixel-corner tl"></div><div class="pixel-corner tr"></div>
+                                                        <div class="pixel-corner bl"></div><div class="pixel-corner br"></div>
+                                                    </div>
+                                                    <div class="pixel-data-panel">
+                                                        <div class="pixel-data-filename"><i class="bi bi-check-circle-fill"></i><span id="carrierFileName">image.jpg</span></div>
+                                                        <div class="pixel-data-row"><span class="pixel-status-badge">Carrier Loaded</span><span class="pixel-data-value" id="carrierFileSize">--</span></div>
+                                                        <div class="pixel-dimensions" id="carrierDims">-- x -- px</div>
+                                                    </div>
                                                 </div>
+                                                <div class="form-text">Image to hide your message in</div>
+                                            </div>
+
+                                            <!-- Audio Carrier (hidden by default, shown when audio type selected) -->
+                                            <div class="d-none" id="audioCarrierSection">
+                                                <label class="form-label">
+                                                    <i class="bi bi-file-earmark-music me-1"></i> Carrier Audio
+                                                </label>
+                                                <div class="drop-zone pixel-container" id="audioCarrierDropZone">
+                                                    <input type="file" name="carrier" accept="audio/*" id="audioCarrierInput">
+                                                    <div class="drop-zone-label">
+                                                        <i class="bi bi-music-note-beamed fs-3 d-block mb-2 text-muted"></i>
+                                                        <span class="text-muted">Drop audio or click</span>
+                                                    </div>
+                                                    <div class="pixel-data-panel">
+                                                        <div class="pixel-data-filename"><i class="bi bi-check-circle-fill"></i><span id="audioCarrierFileName">audio.wav</span></div>
+                                                        <div class="pixel-data-row"><span class="pixel-status-badge">Audio Loaded</span><span class="pixel-data-value" id="audioCarrierFileSize">--</span></div>
+                                                        <div class="pixel-dimensions" id="audioCarrierDuration">--:-- duration</div>
+                                                    </div>
+                                                </div>
+                                                <div class="form-text">Audio file to hide your message in</div>
                                             </div>
-                                            <div class="form-text">Image to hide your message in</div>
                                         </div>
                                     </div>
 
@@ -204,30 +267,54 @@
                                         </div>
                                     </div>
 
-                                    <!-- Embedding Mode (compact inline) -->
-                                    <div class="d-flex gap-2 align-items-center flex-wrap mb-2">
-                                        <div class="btn-group btn-group-sm" role="group">
-                                            <input type="radio" class="btn-check" name="embed_mode" id="modeDct" value="dct" {% if has_dct %}checked{% endif %} {% if not has_dct %}disabled{% endif %}>
-                                            <label class="btn btn-outline-secondary btn-sm text-nowrap" for="modeDct" id="dctModeLabel"><i class="bi bi-soundwave me-1"></i>DCT</label>
-                                            <input type="radio" class="btn-check" name="embed_mode" id="modeLsb" value="lsb" {% if not has_dct %}checked{% endif %}>
-                                            <label class="btn btn-outline-secondary btn-sm text-nowrap" for="modeLsb"><i class="bi bi-grid-3x3-gap me-1"></i>LSB</label>
+                                    <!-- Audio Capacity Info (v4.3.0) -->
+                                    <div class="alert alert-info small d-none mb-3" id="audioCapacityPanel">
+                                        <div class="d-flex justify-content-between align-items-center">
+                                            <span><i class="bi bi-music-note-beamed me-1"></i><span id="audioInfo">-</span></span>
+                                            <span>
+                                                <span class="badge bg-primary me-1" id="lsbAudioCapacityBadge">LSB: -</span>
+                                                <span class="badge bg-warning text-dark" id="spreadCapacityBadge">Spread: -</span>
+                                            </span>
                                         </div>
-                                        <span class="text-muted d-none d-sm-inline">|</span>
-                                        <span class="d-flex gap-2 align-items-center" id="outputOptions">
-                                            <div class="btn-group btn-group-sm" role="group">
-                                                <input type="radio" class="btn-check" name="dct_color_mode" id="colorMode" value="color" checked>
-                                                <label class="btn btn-outline-secondary btn-sm" for="colorMode">Color</label>
-                                                <input type="radio" class="btn-check" name="dct_color_mode" id="grayMode" value="grayscale">
-                                                <label class="btn btn-outline-secondary btn-sm" for="grayMode" id="grayModeLabel">Gray</label>
-                                            </div>
-                                            <div class="btn-group btn-group-sm" role="group">
-                                                <input type="radio" class="btn-check" name="dct_output_format" id="jpegFormat" value="jpeg" checked>
-                                                <label class="btn btn-outline-secondary btn-sm" for="jpegFormat" id="jpegFormatLabel">JPEG</label>
-                                                <input type="radio" class="btn-check" name="dct_output_format" id="pngFormat" value="png">
-                                                <label class="btn btn-outline-secondary btn-sm" for="pngFormat">PNG</label>
-                                            </div>
-                                        </span>
                                     </div>
+
+                                    <!-- Embedding Mode (compact inline) -->
+                                    <div id="imageModeGroup">
+                                        <div class="d-flex gap-2 align-items-center flex-wrap mb-2">
+                                            <div class="btn-group btn-group-sm" role="group">
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeDct" value="dct" {% if has_dct %}checked{% endif %} {% if not has_dct %}disabled{% endif %}>
+                                                <label class="btn btn-outline-secondary btn-sm text-nowrap" for="modeDct" id="dctModeLabel"><i class="bi bi-soundwave me-1"></i>DCT</label>
+                                                <input type="radio" class="btn-check" name="embed_mode" id="modeLsb" value="lsb" {% if not has_dct %}checked{% endif %}>
+                                                <label class="btn btn-outline-secondary btn-sm text-nowrap" for="modeLsb"><i class="bi bi-grid-3x3-gap me-1"></i>LSB</label>
+                                            </div>
+                                            <span class="text-muted d-none d-sm-inline">|</span>
+                                            <span class="d-flex gap-2 align-items-center" id="outputOptions">
+                                                <div class="btn-group btn-group-sm" role="group">
+                                                    <input type="radio" class="btn-check" name="dct_color_mode" id="colorMode" value="color" checked>
+                                                    <label class="btn btn-outline-secondary btn-sm" for="colorMode">Color</label>
+                                                    <input type="radio" class="btn-check" name="dct_color_mode" id="grayMode" value="grayscale">
+                                                    <label class="btn btn-outline-secondary btn-sm" for="grayMode" id="grayModeLabel">Gray</label>
+                                                </div>
+                                                <div class="btn-group btn-group-sm" role="group">
+                                                    <input type="radio" class="btn-check" name="dct_output_format" id="jpegFormat" value="jpeg" checked>
+                                                    <label class="btn btn-outline-secondary btn-sm" for="jpegFormat" id="jpegFormatLabel">JPEG</label>
+                                                    <input type="radio" class="btn-check" name="dct_output_format" id="pngFormat" value="png">
+                                                    <label class="btn btn-outline-secondary btn-sm" for="pngFormat">PNG</label>
+                                                </div>
+                                            </span>
+                                        </div>
+                                    </div>
+
+                                    <!-- Audio Modes (hidden by default) -->
+                                    <div class="d-none" id="audioModeGroup">
+                                        <div class="btn-group btn-group-sm" role="group">
+                                            <input type="radio" class="btn-check" name="embed_mode" id="modeAudioLsb" value="audio_lsb">
+                                            <label class="btn btn-outline-secondary btn-sm text-nowrap" for="modeAudioLsb"><i class="bi bi-grid-3x3-gap me-1"></i>LSB</label>
+                                            <input type="radio" class="btn-check" name="embed_mode" id="modeAudioSpread" value="audio_spread">
+                                            <label class="btn btn-outline-secondary btn-sm text-nowrap" for="modeAudioSpread"><i class="bi bi-broadcast me-1"></i>Spread</label>
+                                        </div>
+                                    </div>
+
                                     <div class="form-text" id="modeHint">
                                         <i class="bi bi-{% if has_dct %}phone{% else %}hdd{% endif %} me-1"></i>{% if has_dct %}Survives social media compression{% else %}Higher capacity for direct transfers{% endif %}
                                     </div>
@@ -237,13 +324,13 @@
                         </div>
 
                         <!-- ================================================================
-                             STEP 2: PAYLOAD
+                             STEP 3: PAYLOAD
                              ================================================================ -->
                         <div class="accordion-item">
                             <h2 class="accordion-header">
                                 <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#stepPayload">
                                     <span class="step-title">
-                                        <span class="step-number" id="stepPayloadNumber">2</span>
+                                        <span class="step-number" id="stepPayloadNumber">3</span>
                                         <i class="bi bi-box me-1"></i> Payload
                                     </span>
                                     <span class="step-summary" id="stepPayloadSummary">Message or file to hide</span>
@@ -295,13 +382,13 @@
                         </div>
 
                         <!-- ================================================================
-                             STEP 3: SECURITY
+                             STEP 4: SECURITY
                              ================================================================ -->
                         <div class="accordion-item">
                             <h2 class="accordion-header">
                                 <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#stepSecurity">
                                     <span class="step-title">
-                                        <span class="step-number" id="stepSecurityNumber">3</span>
+                                        <span class="step-number" id="stepSecurityNumber">4</span>
                                         <i class="bi bi-shield-lock me-1"></i> Security
                                     </span>
                                     <span class="step-summary" id="stepSecuritySummary">Passphrase & keys</span>
@@ -462,13 +549,131 @@ document.querySelectorAll('input[name="embed_mode"]').forEach(radio => {
     });
 });
 
+// ============================================================================
+// CARRIER TYPE TOGGLE (v4.3.0)
+// ============================================================================
+
+const carrierTypeRadios = document.querySelectorAll('input[name="carrier_type_select"]');
+const carrierTypeInput = document.getElementById('carrierTypeInput');
+const imageCarrierSection = document.getElementById('imageCarrierSection');
+const audioCarrierSection = document.getElementById('audioCarrierSection');
+const imageModeGroup = document.getElementById('imageModeGroup');
+const audioModeGroup = document.getElementById('audioModeGroup');
+const capacityPanel = document.getElementById('capacityPanel');
+const audioCapacityPanel = document.getElementById('audioCapacityPanel');
+const stepCarrierTypeSummary = document.getElementById('stepCarrierTypeSummary');
+
+carrierTypeRadios.forEach(radio => {
+    radio.addEventListener('change', function() {
+        const isAudio = this.value === 'audio';
+        carrierTypeInput.value = this.value;
+
+        // Toggle carrier sections
+        if (imageCarrierSection) imageCarrierSection.classList.toggle('d-none', isAudio);
+        if (audioCarrierSection) audioCarrierSection.classList.toggle('d-none', !isAudio);
+
+        // Toggle required attribute so hidden inputs don't block form submission
+        const imgCarrier = document.getElementById('carrierInput');
+        const audCarrier = document.getElementById('audioCarrierInput');
+        if (imgCarrier) { if (isAudio) imgCarrier.removeAttribute('required'); else imgCarrier.setAttribute('required', ''); }
+        if (audCarrier) { if (isAudio) audCarrier.setAttribute('required', ''); else audCarrier.removeAttribute('required'); }
+
+        // Toggle mode groups
+        if (imageModeGroup) imageModeGroup.classList.toggle('d-none', isAudio);
+        if (audioModeGroup) audioModeGroup.classList.toggle('d-none', !isAudio);
+
+        // Toggle capacity panels
+        if (capacityPanel) capacityPanel.classList.add('d-none');
+        if (audioCapacityPanel) audioCapacityPanel.classList.add('d-none');
+
+        // Update summary
+        if (stepCarrierTypeSummary) {
+            stepCarrierTypeSummary.textContent = isAudio ? 'Audio' : 'Image';
+        }
+
+        // Select default mode for the active type
+        if (isAudio) {
+            const audioLsb = document.getElementById('modeAudioLsb');
+            if (audioLsb) audioLsb.checked = true;
+        } else {
+            // Reset to DCT if available, else LSB
+            const dctRadio = document.getElementById('modeDct');
+            const lsbRadio = document.getElementById('modeLsb');
+            if (dctRadio && !dctRadio.disabled) {
+                dctRadio.checked = true;
+            } else if (lsbRadio) {
+                lsbRadio.checked = true;
+            }
+        }
+
+        // Clear carrier file selections
+        const carrierInput = document.getElementById('carrierInput');
+        const audioCarrierInput = document.getElementById('audioCarrierInput');
+        if (carrierInput) carrierInput.value = '';
+        if (audioCarrierInput) audioCarrierInput.value = '';
+
+        // Reset previews
+        document.getElementById('carrierPreview')?.classList.add('d-none');
+
+        // Update step title
+        const stepImagesTitle = document.querySelector('#stepImages')?.closest('.accordion-item')?.querySelector('.accordion-button .step-title');
+        if (stepImagesTitle) {
+            const icon = stepImagesTitle.querySelector('i:not(.step-number i)');
+            const textNode = stepImagesTitle.childNodes[stepImagesTitle.childNodes.length - 1];
+            if (icon) {
+                icon.className = isAudio ? 'bi bi-music-note-beamed me-1' : 'bi bi-images me-1';
+            }
+        }
+
+        updateImagesSummary();
+    });
+});
+
+// Audio carrier file change handler
+const audioCarrierInput = document.getElementById('audioCarrierInput');
+audioCarrierInput?.addEventListener('change', function() {
+    if (this.files && this.files[0]) {
+        const file = this.files[0];
+        document.getElementById('audioCarrierFileName').textContent = file.name;
+        document.getElementById('audioCarrierFileSize').textContent = (file.size / 1024).toFixed(1) + ' KB';
+
+        // Fetch audio capacity
+        const formData = new FormData();
+        formData.append('carrier', file);
+        fetch('/api/audio-capacity', { method: 'POST', body: formData })
+            .then(r => r.json())
+            .then(data => {
+                if (data.error) return;
+                const info = `${data.format || 'Audio'} · ${data.sample_rate}Hz · ${data.channels}ch · ${data.duration}s`;
+                document.getElementById('audioInfo').textContent = info;
+                document.getElementById('lsbAudioCapacityBadge').textContent = `LSB: ${(data.lsb_capacity / 1024).toFixed(1)} KB`;
+                document.getElementById('spreadCapacityBadge').textContent = `Spread: ${(data.spread_capacity / 1024).toFixed(1)} KB`;
+                document.getElementById('audioCapacityPanel')?.classList.remove('d-none');
+                if (data.duration) {
+                    document.getElementById('audioCarrierDuration').textContent = data.duration + 's duration';
+                }
+            }).catch(() => {});
+
+        // Trigger the drop zone animation
+        const dropZone = document.getElementById('audioCarrierDropZone');
+        if (dropZone) {
+            dropZone.classList.add('has-file');
+        }
+
+        updateImagesSummary();
+    }
+});
+
 // ============================================================================
 // ACCORDION SUMMARY UPDATES
 // ============================================================================
 
 function updateImagesSummary() {
     const ref = document.getElementById('refPhotoInput')?.files[0];
-    const carrier = document.getElementById('carrierInput')?.files[0];
+    const isAudio = carrierTypeInput?.value === 'audio';
+    const carrier = isAudio
+        ? document.getElementById('audioCarrierInput')?.files[0]
+        : document.getElementById('carrierInput')?.files[0];
     const mode = document.querySelector('input[name="embed_mode"]:checked')?.value?.toUpperCase() || 'LSB';
     const summary = document.getElementById('stepImagesSummary');
     const stepNum = document.getElementById('stepImagesNumber');
@@ -484,12 +689,12 @@ function updateImagesSummary() {
         summary.textContent = ref ? ref.name.slice(0, 15) : carrier.name.slice(0, 15);
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '1';
+        stepNum.textContent = '2';
     } else {
-        summary.textContent = 'Select reference & carrier';
+        summary.textContent = isAudio ? 'Select reference & audio' : 'Select reference & carrier';
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '1';
+        stepNum.textContent = '2';
     }
 }
 
@@ -515,7 +720,7 @@ function updatePayloadSummary() {
         summary.textContent = 'Message or file to hide';
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '2';
+        stepNum.textContent = '3';
     }
 }
 
@@ -543,14 +748,16 @@ function updateSecuritySummary() {
         summary.textContent = 'Passphrase & keys';
         summary.classList.remove('has-content');
         stepNum.classList.remove('complete');
-        stepNum.textContent = '3';
+        stepNum.textContent = '4';
     }
 }
 
 // Attach listeners
 document.getElementById('refPhotoInput')?.addEventListener('change', updateImagesSummary);
 document.getElementById('carrierInput')?.addEventListener('change', updateImagesSummary);
+document.getElementById('audioCarrierInput')?.addEventListener('change', updateImagesSummary);
 document.querySelectorAll('input[name="embed_mode"]').forEach(r => r.addEventListener('change', updateImagesSummary));
+document.querySelectorAll('#audioModeGroup input[name="embed_mode"]').forEach(r => r.addEventListener('change', updateImagesSummary));
 
 document.getElementById('messageInput')?.addEventListener('input', updatePayloadSummary);
 document.getElementById('payloadFileInput')?.addEventListener('change', updatePayloadSummary);

frontends/web/templates/encode_result.html

@@ -12,12 +12,26 @@
                 </h5>
             </div>
             <div class="card-body text-center">
+                {% if carrier_type == 'audio' %}
+                <!-- Audio Preview -->
+                <div class="my-4">
+                    <div class="text-center">
+                        <i class="bi bi-music-note-beamed text-success" style="font-size: 4rem;"></i>
+                        <div class="mt-2">
+                            <audio controls src="{{ url_for('encode_file_route', file_id=file_id) }}" class="w-100" style="max-width: 400px;"></audio>
+                        </div>
+                        <div class="mt-2 small text-muted">
+                            <i class="bi bi-music-note-beamed me-1"></i>Encoded Audio Preview
+                        </div>
+                    </div>
+                </div>
+                {% else %}
                 <div class="my-4">
                     {% if thumbnail_url %}
                     <!-- Thumbnail of the actual encoded image -->
                     <div class="encoded-image-thumbnail">
-                        <img src="{{ thumbnail_url }}" 
-                             alt="Encoded image thumbnail" 
+                        <img src="{{ thumbnail_url }}"
+                             alt="Encoded image thumbnail"
                              class="img-thumbnail rounded"
                              style="max-width: 250px; max-height: 250px; object-fit: contain;">
                         <div class="mt-2 small text-muted">
@@ -29,8 +43,9 @@
                     <i class="bi bi-file-earmark-image text-success" style="font-size: 4rem;"></i>
                     {% endif %}
                 </div>
+                {% endif %}
                 
-                <p class="lead mb-4">Your secret has been hidden in the image.</p>
+                <p class="lead mb-4">Your secret has been hidden in the {{ 'audio file' if carrier_type == 'audio' else 'image' }}.</p>
                 
                 <div class="mb-3">
                     <code class="fs-5">{{ filename }}</code>
@@ -38,11 +53,32 @@
                 
                 <!-- Mode and format badges -->
                 <div class="mb-4">
-                    {% if embed_mode == 'dct' %}
+                    {% if carrier_type == 'audio' %}
+                    <!-- Audio mode badges -->
+                    {% if embed_mode == 'audio_spread' %}
+                    <span class="badge bg-warning text-dark fs-6">
+                        <i class="bi bi-broadcast me-1"></i>Spread Spectrum
+                    </span>
+                    {% else %}
+                    <span class="badge bg-primary fs-6">
+                        <i class="bi bi-grid-3x3-gap me-1"></i>Audio LSB
+                    </span>
+                    {% endif %}
+                    <span class="badge bg-info fs-6 ms-1">
+                        <i class="bi bi-file-earmark-music me-1"></i>WAV
+                    </span>
+                    <div class="small text-muted mt-2">
+                        {% if embed_mode == 'audio_spread' %}
+                        Spread spectrum embedding in audio samples
+                        {% else %}
+                        LSB embedding in audio samples, WAV output
+                        {% endif %}
+                    </div>
+                    {% elif embed_mode == 'dct' %}
                         <span class="badge bg-info fs-6">
                             <i class="bi bi-soundwave me-1"></i>DCT Mode
                         </span>
-                        
+
                         <!-- Color mode badge (v3.0.1) -->
                         {% if color_mode == 'color' %}
                         <span class="badge bg-success fs-6 ms-1">
@@ -53,7 +89,7 @@
                             <i class="bi bi-circle-half me-1"></i>Grayscale
                         </span>
                         {% endif %}
-                        
+
                         <!-- Output format badge -->
                         {% if output_format == 'jpeg' %}
                         <span class="badge bg-warning text-dark fs-6 ms-1">
@@ -78,7 +114,7 @@
                             {% endif %}
                         </div>
                         {% endif %}
-                        
+
                     {% else %}
                         <span class="badge bg-primary fs-6">
                             <i class="bi bi-grid-3x3-gap me-1"></i>LSB Mode
@@ -114,7 +150,7 @@
                 <div class="d-grid gap-2">
                     <a href="{{ url_for('encode_download', file_id=file_id) }}" 
                        class="btn btn-primary btn-lg" id="downloadBtn">
-                        <i class="bi bi-download me-2"></i>Download Image
+                        <i class="bi bi-download me-2"></i>Download {{ 'Audio' if carrier_type == 'audio' else 'Image' }}
                     </a>
                     
                     <button type="button" class="btn btn-outline-primary" id="shareBtn" style="display: none;">
@@ -129,6 +165,11 @@
                     <strong>Important:</strong>
                     <ul class="mb-0 mt-2">
                         <li>This file expires in <strong>10 minutes</strong></li>
+                        {% if carrier_type == 'audio' %}
+                        <li>Do <strong>not</strong> re-encode or convert the audio file</li>
+                        <li>WAV format preserves your hidden data losslessly</li>
+                        <li>Sharing via platforms that re-encode audio will destroy the hidden data</li>
+                        {% else %}
                         <li>Do <strong>not</strong> resize or recompress the image</li>
                         {% if embed_mode == 'dct' and output_format == 'jpeg' %}
                         <li>JPEG format is lossy - avoid re-saving or editing</li>
@@ -141,6 +182,7 @@
                         <li>Color preserved - extraction works on both color and grayscale</li>
                         {% endif %}
                         {% endif %}
+                        {% endif %}
                         {% if channel_mode == 'private' %}
                         <li><i class="bi bi-shield-lock text-warning me-1"></i>Recipient needs the <strong>same channel key</strong> to decode</li>
                         {% endif %}
@@ -148,7 +190,7 @@
                 </div>
                 
                 <a href="{{ url_for('encode_page') }}" class="btn btn-outline-secondary">
-                    <i class="bi bi-arrow-repeat me-2"></i>Encode Another Message
+                    <i class="bi bi-arrow-repeat me-2"></i>Encode Another
                 </a>
             </div>
         </div>
@@ -162,7 +204,7 @@
 const shareBtn = document.getElementById('shareBtn');
 const fileUrl = "{{ url_for('encode_file_route', file_id=file_id, _external=True) }}";
 const fileName = "{{ filename }}";
-const mimeType = "{{ 'image/jpeg' if embed_mode == 'dct' and output_format == 'jpeg' else 'image/png' }}";
+const mimeType = "{{ 'audio/wav' if carrier_type == 'audio' else ('image/jpeg' if embed_mode == 'dct' and output_format == 'jpeg' else 'image/png') }}";
 
 if (navigator.share && navigator.canShare) {
     // Check if we can share files