feat: add smart audio copy and audio mix presets for configurable 5.1 downmixing

server/routes/probe.js

@@ -128,6 +128,7 @@ function analyzeProbeResult(probeResult, url) {
     return {
         video: videoCodec,
         audio: audioCodec,
+        audioChannels: audioStream?.channels || 0, // For Smart Audio Copy
         container: container,
         compatible: compatible,
         needsRemux: needsRemux,

server/routes/transcode.js

@@ -29,7 +29,7 @@ transcodeSession.startCleanupInterval();
  * Body: { url: string, seekOffset?: number }
  */
 router.post('/session', async (req, res) => {
-    const { url, seekOffset, videoMode, videoCodec } = req.body;
+    const { url, seekOffset, videoMode, videoCodec, audioCodec, audioChannels } = req.body;
 
     if (!url) {
         return res.status(400).json({ error: 'URL is required' });
@@ -47,8 +47,11 @@ router.post('/session', async (req, res) => {
             hwEncoder: settings.hwEncoder || 'software',
             maxResolution: settings.maxResolution || '1080p',
             quality: settings.quality || 'medium',
+            audioMixPreset: settings.audioMixPreset || 'auto', // Audio downmix preset
             videoMode: videoMode, // 'copy' or 'encode'
-            videoCodec: videoCodec // 'h264', 'hevc', etc.
+            videoCodec: videoCodec, // 'h264', 'hevc', etc.
+            audioCodec: audioCodec, // 'aac', 'ac3', etc.
+            audioChannels: audioChannels // number of channels (2=stereo)
         });
 
         await session.start();