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

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;