Linux: render video via HTML5 WebView instead of the MPV backend

- online.rs: on Linux, advertise only WebView-decodable codecs (h264 video;
  aac/mp3/opus/vorbis/flac audio) in PlaybackInfo so Jellyfin transcodes
  HEVC/AV1/VP9/etc. to h264 HLS for the WebKitGTK <video> element.
- player: on Linux, don't load video into MPV (no embedded window — it would
  start a redundant decode the frontend immediately stops). Add
  PlayerController::set_current_item to keep queue/UI/remote-transfer state in
  sync without loading the item into the playback backend.

src-tauri/src/commands/player/mod.rs

@@ -411,9 +411,22 @@ pub async fn player_play_item(
     }
 
     let controller = player.0.lock().await;
+    // On Linux, video plays in the WebKitGTK HTML5 <video> element (see
+    // get_player_status -> use_html5_element). The MPV backend has no embedded
+    // window, so loading the stream into it would only start a redundant decode
+    // (and the frontend would immediately stop it). Only load into the native
+    // backend on platforms that actually render video through it (e.g. Android).
+    #[cfg(not(target_os = "linux"))]
     controller
         .play_item(media_item)
         .map_err(|e| e.to_string())?;
+    #[cfg(target_os = "linux")]
+    {
+        // Keep the queue in sync for UI/remote-transfer without starting MPV.
+        controller
+            .set_current_item(media_item)
+            .map_err(|e| e.to_string())?;
+    }
 
     // Emit queue changed event
     controller.emit_queue_changed();

src-tauri/src/player/mod.rs

@@ -212,6 +212,22 @@ impl PlayerController {
         Ok(())
     }
 
+    /// Set the current queue item without loading it into the playback backend.
+    ///
+    /// Used on platforms where video is rendered outside the native backend
+    /// (Linux WebKitGTK HTML5 <video>): the queue/UI state must reflect the
+    /// item, but MPV must not start a redundant decode for it.
+    pub fn set_current_item(&self, item: MediaItem) -> Result<(), PlayerError> {
+        debug!("[PlayerController] set_current_item (no backend load): {}", item.title);
+
+        self.reset_autoplay_count();
+
+        let mut queue = self.queue.lock_safe();
+        queue.set_queue(vec![item], 0);
+
+        Ok(())
+    }
+
     /// Load and play an item without modifying the queue
     /// Use this when the queue is already set up and you just want to play a specific item from it
     pub fn load_and_play(&self, item: &MediaItem) -> Result<(), PlayerError> {

src-tauri/src/repository/online.rs

@@ -859,7 +859,18 @@ impl MediaRepository for OnlineRepository {
                 ("h264,hevc".to_string(), "aac,mp3".to_string())
             });
 
-        #[cfg(not(target_os = "android"))]
+        // Linux desktop plays video through the WebKitGTK HTML5 <video> element,
+        // which cannot reliably decode HEVC/AV1/VP9. Advertise only codecs the
+        // WebView can decode so Jellyfin transcodes anything else to h264 HLS.
+        // (Audio-only files still direct-play via MPV, but the PlaybackInfo
+        // profile is shared, so we keep the broadly-supported audio codecs.)
+        #[cfg(all(not(target_os = "android"), target_os = "linux"))]
+        let (video_codecs, audio_codecs) = (
+            "h264".to_string(),
+            "aac,mp3,opus,vorbis,flac".to_string(),
+        );
+
+        #[cfg(all(not(target_os = "android"), not(target_os = "linux")))]
         let (video_codecs, audio_codecs) = (
             "h264,hevc,vp8,vp9,av1,mpeg4".to_string(),
             "aac,mp3,opus,vorbis,flac".to_string(),