fix(playback): bound the device profile by the audio route's channels (DR-141)

MediaCodecList answers "can this device decode 5.1", which is not the
question that decides whether the user hears anything: a phone decodes an
AC-3 5.1 track happily and still has two channels to play it out of. The
DeviceProfile carried no MaxAudioChannels, so Jellyfin was free to
direct-play the multichannel track to a two-channel sink — silence or
dialogue folded into surround channels that go nowhere, depending on the
device.

Report media3 AudioCapabilities.maxChannelCount for the current route over
JNI alongside the codec lists, and bound the direct-play and transcoding
profiles (and the HLS URL's TranscodingMaxAudioChannels, previously
hardcoded to 2) by it. No codec is ever removed, so a device with genuine
surround output keeps direct-playing it. A missing or zero reading means
"route not yet established", not "no audio", and falls back to stereo.

src-tauri/src/repository/online.rs

@@ -404,7 +404,10 @@ impl OnlineRepository {
             ("MaxStreamingBitrate", "20000000".to_string()),
             ("VideoBitrate", "18000000".to_string()),
             ("AudioBitrate", "384000".to_string()),
-            ("TranscodingMaxAudioChannels", "2".to_string()),
+            (
+                "TranscodingMaxAudioChannels",
+                super::device_profile::max_audio_channels().to_string(),
+            ),
             ("SegmentContainer", "ts".to_string()),
             ("TranscodingContainer", "ts".to_string()),
             ("TranscodingProtocol", "hls".to_string()),
@@ -1271,6 +1274,10 @@ impl MediaRepository for OnlineRepository {
             name: String,
             max_streaming_bitrate: i64,
             max_static_bitrate: i64,
+            /// Channels the device's audio route can actually voice. Without it
+            /// the server may direct-play a 5.1 track to a two-channel sink,
+            /// which is silence or inaudible dialogue depending on the device.
+            max_audio_channels: String,
             direct_play_profiles: Vec<DirectPlayProfile>,
             transcoding_profiles: Vec<TranscodingProfile>,
             subtitle_profiles: Vec<SubtitleProfile>,
@@ -1298,6 +1305,7 @@ impl MediaRepository for OnlineRepository {
             #[serde(skip_serializing_if = "Option::is_none")]
             video_codec: Option<String>,
             audio_codec: String,
+            max_audio_channels: String,
         }
 
         #[derive(Debug, Serialize)]
@@ -1338,8 +1346,9 @@ impl MediaRepository for OnlineRepository {
 
         // Get detected codecs from Android MediaCodecList or use platform defaults
         #[cfg(target_os = "android")]
-        let (video_codecs, audio_codecs) =
-            crate::player::get_detected_codecs().unwrap_or_else(|| {
+        let (video_codecs, audio_codecs) = crate::player::get_detected_codecs()
+            .map(|(video, audio, _channels)| (video, audio))
+            .unwrap_or_else(|| {
                 warn!("[DeviceProfile] Codec detection not complete, using conservative defaults");
                 ("h264,hevc".to_string(), "aac,mp3".to_string())
             });
@@ -1362,11 +1371,18 @@ impl MediaRepository for OnlineRepository {
         info!("[DeviceProfile] Using video codecs: {}", video_codecs);
         info!("[DeviceProfile] Using audio codecs: {}", audio_codecs);
 
+        // Bound every profile by what the audio route can actually voice, so a
+        // multichannel track is downmixed by the server rather than direct-played
+        // into a sink that has nowhere to put the extra channels.
+        let max_audio_channels = super::device_profile::max_audio_channels().to_string();
+        info!("[DeviceProfile] Max audio channels: {}", max_audio_channels);
+
         // Create device profile with detected hardware capabilities
         let device_profile = DeviceProfile {
             name: "JellyTau Native Player".to_string(),
             max_streaming_bitrate: 999_999_999,
             max_static_bitrate: 999_999_999,
+            max_audio_channels: max_audio_channels.clone(),
             direct_play_profiles: vec![
                 DirectPlayProfile {
                     profile_type: "Video".to_string(),
@@ -1389,6 +1405,7 @@ impl MediaRepository for OnlineRepository {
                     container: "ts".to_string(),
                     video_codec: Some("h264,hevc".to_string()),
                     audio_codec: "aac,mp3".to_string(),
+                    max_audio_channels: max_audio_channels.clone(),
                 },
                 TranscodingProfile {
                     profile_type: "Audio".to_string(),
@@ -1397,6 +1414,7 @@ impl MediaRepository for OnlineRepository {
                     container: "mp3".to_string(),
                     video_codec: None,
                     audio_codec: "mp3".to_string(),
+                    max_audio_channels: max_audio_channels.clone(),
                 },
             ],
             subtitle_profiles: vec![