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

public/index.html

@@ -548,6 +548,20 @@
                   <option value="low">Low (Fastest)</option>
                 </select>
               </div>
+              <div class="setting-item">
+                <div class="setting-info" style="flex: 1;">
+                  <span class="setting-label">Audio Mix Preset</span>
+                  <span class="setting-hint">How multi-channel audio (5.1/7.1) is mixed down to stereo for browser
+                    playback.</span>
+                </div>
+                <select id="setting-audio-mix" class="source-select" style="width: auto; min-width: 200px;">
+                  <option value="auto">Auto (Smart Copy/ITU)</option>
+                  <option value="itu">ITU-R BS.775 (Balanced)</option>
+                  <option value="night">Night Mode (Dialogue Boost)</option>
+                  <option value="cinematic">Cinematic (Wide)</option>
+                  <option value="passthrough">Passthrough (Copy)</option>
+                </select>
+              </div>
             </div>
 
             <div class="settings-section">

public/js/components/VideoPlayer.js

@@ -806,7 +806,12 @@ class VideoPlayer {
                         const statusText = videoMode === 'copy' ? 'Transcoding (Audio)' : 'Transcoding (Video)';
 
                         this.updateTranscodeStatus('transcoding', statusText);
-                        const playlistUrl = await this.startTranscodeSession(streamUrl, { videoMode, videoCodec: info.video });
+                        const playlistUrl = await this.startTranscodeSession(streamUrl, {
+                            videoMode,
+                            videoCodec: info.video,
+                            audioCodec: info.audio,
+                            audioChannels: info.audioChannels
+                        });
                         this.currentUrl = playlistUrl; // Update currentUrl for HLS reload
 
                         this.playHls(playlistUrl);

public/js/pages/Settings.js

@@ -149,6 +149,16 @@ class SettingsPage {
             this.app.player.saveSettings();
         });
 
+        // Audio Mix Preset
+        const audioMixSelect = document.getElementById('setting-audio-mix');
+        if (audioMixSelect) {
+            audioMixSelect.value = this.app.player?.settings?.audioMixPreset || 'auto';
+            audioMixSelect.addEventListener('change', () => {
+                this.app.player.settings.audioMixPreset = audioMixSelect.value;
+                this.app.player.saveSettings();
+            });
+        }
+
         // Stream processing toggles
         forceProxyToggle?.addEventListener('change', () => {
             this.app.player.settings.forceProxy = forceProxyToggle.checked;

public/js/pages/WatchPage.js

@@ -330,7 +330,12 @@ class WatchPage {
                     const statusText = videoMode === 'copy' ? 'Transcoding (Audio)' : 'Transcoding (Video)';
 
                     this.updateTranscodeStatus('transcoding', statusText);
-                    const playlistUrl = await this.startTranscodeSession(url, { videoMode, videoCodec: info.video });
+                    const playlistUrl = await this.startTranscodeSession(url, {
+                        videoMode,
+                        videoCodec: info.video,
+                        audioCodec: info.audio,
+                        audioChannels: info.audioChannels
+                    });
                     this.playHls(playlistUrl);
                     this.setVolumeFromStorage();
                     return;