feat: add audio channel configuration for MPV player

- Add audio channels setting (auto/mono/stereo) to MPV properties
- Implement UI controls in settings panel and player right controls
- Enable immediate MPV property application when setting changes
- Update default playback type to LOCAL and sample rate to 48kHz

src/renderer/features/player/components/right-controls.tsx

@@ -36,6 +36,7 @@ import { PlaybackType } from '/@/shared/types/types';
 
 const ipc = isElectron() ? window.api.ipc : null;
 const remote = isElectron() ? window.api.remote : null;
+const mpvPlayer = isElectron() ? window.api.mpvPlayer : null;
 
 export const RightControls = () => {
     const { t } = useTranslation();
@@ -218,6 +219,46 @@ export const RightControls = () => {
                 )}
             </Group>
             <Group align="center" gap="xs" wrap="nowrap">
+                {(playbackType === PlaybackType.LOCAL || playbackType === PlaybackType.WEB) && (
+                    <ActionIcon
+                        icon={
+                            playbackSettings.mpvProperties.audioChannels === 'mono'
+                                ? 'volumeNormal'
+                                : 'volumeMax'
+                        }
+                        iconProps={{
+                            size: 'lg',
+                        }}
+                        onClick={(e) => {
+                            e.stopPropagation();
+                            const current =
+                                playbackSettings.mpvProperties.audioChannels || 'stereo';
+                            const next = current === 'mono' ? 'stereo' : 'mono';
+                            setSettings({
+                                playback: {
+                                    ...playbackSettings,
+                                    mpvProperties: {
+                                        ...playbackSettings.mpvProperties,
+                                        audioChannels: next,
+                                    },
+                                },
+                            });
+                            // Apply to MPV immediately
+                            mpvPlayer?.setProperties({
+                                'audio-channels': next,
+                            });
+                        }}
+                        size="sm"
+                        tooltip={{
+                            label:
+                                playbackType === PlaybackType.WEB
+                                    ? `Audio: ${playbackSettings.mpvProperties.audioChannels || 'stereo'} (MPV only)`
+                                    : `Audio: ${playbackSettings.mpvProperties.audioChannels || 'stereo'}`,
+                            openDelay: 0,
+                        }}
+                        variant="subtle"
+                    />
+                )}
                 <DropdownMenu arrowOffset={12} offset={0} position="top-end" width={425} withArrow>
                     <DropdownMenu.Target>
                         <ActionIcon

src/renderer/features/settings/components/playback/mpv-settings.tsx

@@ -32,6 +32,8 @@ export const getMpvSetting = (
     value: any,
 ) => {
     switch (key) {
+        case 'audioChannels':
+            return { 'audio-channels': value };
         case 'audioExclusiveMode':
             return { 'audio-exclusive': value || 'no' };
         case 'audioSampleRateHz':
@@ -53,6 +55,7 @@ export const getMpvSetting = (
 
 export const getMpvProperties = (settings: SettingsState['playback']['mpvProperties']) => {
     const properties: Record<string, any> = {
+        'audio-channels': settings.audioChannels || 'stereo',
         'audio-exclusive': settings.audioExclusiveMode || 'no',
         'audio-samplerate':
             settings.audioSampleRateHz === 0 ? undefined : settings.audioSampleRateHz,
@@ -271,6 +274,22 @@ export const MpvSettings = () => {
             isHidden: settings.type !== PlaybackType.LOCAL,
             title: t('setting.gaplessAudio', { postProcess: 'sentenceCase' }),
         },
+        {
+            control: (
+                <Select
+                    data={[
+                        { label: 'Mono', value: 'mono' },
+                        { label: 'Stereo', value: 'stereo' },
+                    ]}
+                    defaultValue={settings.mpvProperties.audioChannels || 'stereo'}
+                    onChange={(e) => handleSetMpvProperty('audioChannels', e)}
+                />
+            ),
+            description:
+                'Select the audio channel mode. Stereo is the default, mono downmixes to a single channel.',
+            isHidden: settings.type !== PlaybackType.LOCAL,
+            title: 'Audio Channels',
+        },
         {
             control: (
                 <NumberInput

src/renderer/store/settings.store.ts

@@ -124,6 +124,7 @@ const TranscodingConfigSchema = z.object({
 });
 
 const MpvSettingsSchema = z.object({
+    audioChannels: z.enum(['mono', 'stereo']).optional(),
     audioExclusiveMode: z.enum(['no', 'yes']),
     audioFormat: z.enum(['float', 's16', 's32']).optional(),
     audioSampleRateHz: z.number().optional(),
@@ -657,9 +658,10 @@ const initialState: SettingsState = {
         mediaSession: false,
         mpvExtraParameters: [],
         mpvProperties: {
+            audioChannels: 'stereo',
             audioExclusiveMode: 'no',
             audioFormat: undefined,
-            audioSampleRateHz: 0,
+            audioSampleRateHz: 48000,
             gaplessAudio: 'weak',
             replayGainClip: true,
             replayGainFallbackDB: undefined,
@@ -678,7 +680,7 @@ const initialState: SettingsState = {
         transcode: {
             enabled: false,
         },
-        type: PlaybackType.WEB,
+        type: PlaybackType.LOCAL,
         webAudio: true,
     },
     remote: {