fix(plex): subtitles draw only the player's own track, lifted in the player's own pixels

A direct-played file's own subtitle stream (WebKit lists an mp4's mov_text) was switched to hidden and drawn under any choice, Off included: only the player's <track> is kept hidden and read, other subtitle tracks are switched off. The lift was measured in screen pixels and applied inside the x1.25 windowed player, and re-measured off a box carrying its own (or a mid-slide) transform: an untransformed outer box is measured, the distance divided by the scale, and a cue that just appeared is placed, not slid from where the last one was left.

frontend/src/lib/plexPlayerHooks.ts

@@ -18,6 +18,7 @@ import { qk } from "./queryKeys";
 import { useLatest } from "./useLatest";
 import i18n, { plexLang } from "../i18n";
 import { markerSkip } from "./plexMarkers";
+import { ownTextTracks } from "./plexSubTracks";
 import { type PlexPlayerPrefs } from "./plexPlayerPrefs";
 import { PLEX_SCALE, normalizeVolumeIn, stepVolumeIn } from "./playerVolume";
 
@@ -852,23 +853,30 @@ export function usePlexTracks(opts: {
   // sessionK is already lag-compensated (see HlsEngine), so it is the true content-zero the VTT
   // must be shifted by; the user offset nudges on top.
   const subTrackOffset = sessionK - subOffApplied;
-  // Keep every track "hidden": loaded and its cues tracked, but drawn by PlexSubtitles, not by the
-  // browser. Not once per selection: the <track> is remounted on its own key (a grown window, a
-  // retry), and the browser switches a fresh `default` track to "showing" a task later — which drew
-  // the cues a second time, natively, under ours. So it is re-applied on every track the list gains
-  // and on every mode change the browser makes.
+  // Keep our own track "hidden": loaded and its cues tracked, but drawn by PlexSubtitles, not by the
+  // browser. Any other subtitle track (a direct-played file's own, see ownTextTracks) is switched
+  // off, so neither the browser nor PlexSubtitles draws it. Not once per selection: the <track> is
+  // remounted on its own key (a grown window, a retry), and the browser switches a fresh `default`
+  // track to "showing" a task later — which drew the cues a second time, natively, under ours. So it
+  // is re-applied on every track the list gains and on every mode change the browser makes.
   useEffect(() => {
-    const tracks = videoRef.current?.textTracks;
-    if (!tracks) return;
-    const hide = () => {
-      for (const tr of Array.from(tracks)) if (tr.mode !== "hidden") tr.mode = "hidden";
+    const video = videoRef.current;
+    if (!video) return;
+    const tracks = video.textTracks;
+    const settle = () => {
+      const own = ownTextTracks(video);
+      for (const tr of Array.from(tracks)) {
+        const subtitle = tr.kind === "subtitles" || tr.kind === "captions";
+        const want = own.has(tr) ? "hidden" : subtitle ? "disabled" : tr.mode;
+        if (tr.mode !== want) tr.mode = want;
+      }
     };
-    hide();
-    tracks.addEventListener("addtrack", hide);
-    tracks.addEventListener("change", hide);
+    settle();
+    tracks.addEventListener("addtrack", settle);
+    tracks.addEventListener("change", settle);
     return () => {
-      tracks.removeEventListener("addtrack", hide);
-      tracks.removeEventListener("change", hide);
+      tracks.removeEventListener("addtrack", settle);
+      tracks.removeEventListener("change", settle);
     };
   }, [subOrd, id, videoRef]);