feat: Add FFmpeg audio transcoding for Dolby/AC3/EAC3 compatibility

- Add /api/transcode endpoint for audio-only transcoding - Video passthrough (no re-encoding) for fast performance - Audio transcode to AAC for browser compatibility - Add 'Force Audio Transcode' setting toggle in UI - Add ffmpeg-static as optional dependency - Handle Electron asar.unpacked path for packaged apps
2025-12-29 16:52:01 -08:00
parent 61fe03f950
commit 32e0434785
7 changed files with 385 additions and 1 deletions
@@ -0,0 +1,91 @@
+const express = require('express');
+const router = express.Router();
+const { spawn } = require('child_process');
+
+/**
+ * Transcode stream
+ * GET /api/transcode?url=...
+ * 
+ * Transcodes audio to AAC for browser compatibility while passing video through.
+ * This fixes playback issues with Dolby/AC3/EAC3 audio that browsers can't decode.
+ */
+router.get('/', (req, res) => {
+    const { url } = req.query;
+    if (!url) {
+        return res.status(400).json({ error: 'URL parameter is required' });
+    }
+
+    const ffmpegPath = req.app.locals.ffmpegPath || 'ffmpeg';
+    console.log(`[Transcode] Starting transcoding for: ${url}`);
+    console.log(`[Transcode] Using binary: ${ffmpegPath}`);
+
+    // FFmpeg arguments for transcoding
+    // Video: Copy (passthrough) - most sources are already H264/HEVC which browsers support
+    // Audio: Transcode to AAC - fixes Dolby/AC3/EAC3 that browsers can't play
+    const args = [
+        '-hide_banner',
+        '-loglevel', 'info',
+        '-fflags', '+genpts',
+        '-i', url,
+        '-c:v', 'copy', // Video passthrough (no re-encoding = fast!)
+        '-c:a', 'aac',  // Transcode audio to browser-compatible AAC
+        '-ac', '2',
+        '-ar', '48000',
+        '-b:a', '128k',
+        '-af', 'aresample=48000:async=1',
+        // Fragmented MP4 for streaming (browser-compatible)
+        '-f', 'mp4',
+        '-movflags', 'frag_keyframe+empty_moov+default_base_moof',
+        '-' // Output to stdout
+    ];
+
+    console.log(`[Transcode] Full command: ${ffmpegPath} ${args.join(' ')}`);
+
+    let ffmpeg;
+    try {
+        ffmpeg = spawn(ffmpegPath, args);
+    } catch (spawnErr) {
+        console.error('[Transcode] Failed to spawn FFmpeg:', spawnErr);
+        return res.status(500).json({ error: 'FFmpeg spawn failed', details: spawnErr.message });
+    }
+
+    // Collect stderr for error reporting
+    let stderrBuffer = '';
+
+    // Set headers for fragmented MP4
+    res.setHeader('Content-Type', 'video/mp4');
+    res.setHeader('Access-Control-Allow-Origin', '*');
+
+    // Pipe stdout to response
+    ffmpeg.stdout.pipe(res);
+
+    // Log stderr (useful for debugging transcoding failures)
+    ffmpeg.stderr.on('data', (data) => {
+        const msg = data.toString();
+        stderrBuffer += msg;
+        console.log(`[FFmpeg] ${msg}`);
+    });
+
+    // Cleanup on client disconnect
+    req.on('close', () => {
+        console.log('[Transcode] Client disconnected, killing FFmpeg process');
+        ffmpeg.kill('SIGKILL');
+    });
+
+    // Handle process exit
+    ffmpeg.on('exit', (code) => {
+        if (code !== null && code !== 0 && code !== 255) { // 255 is often returned on kill
+            console.error(`[Transcode] FFmpeg exited with code ${code}`);
+        }
+    });
+
+    // Handle spawn errors
+    ffmpeg.on('error', (err) => {
+        console.error('[Transcode] Failed to spawn FFmpeg:', err);
+        if (!res.headersSent) {
+            res.status(500).json({ error: 'Transcoding failed to start' });
+        }
+    });
+});
+
+module.exports = router;