fix(subtitles): normalize local subtitle sentinel to -1 in stream re-negotiation URLs

app/(auth)/player/direct-player.tsx

@@ -25,7 +25,10 @@ import { Controls } from "@/components/video-player/controls/Controls";
 import { Controls as TVControls } from "@/components/video-player/controls/Controls.tv";
 import { PlayerProvider } from "@/components/video-player/controls/contexts/PlayerContext";
 import { VideoProvider } from "@/components/video-player/controls/contexts/VideoContext";
-import { LOCAL_SUBTITLE_INDEX_START } from "@/components/video-player/controls/types";
+import {
+  LOCAL_SUBTITLE_INDEX_START,
+  toServerSubtitleIndex,
+} from "@/components/video-player/controls/types";
 import {
   PlaybackSpeedScope,
   updatePlaybackSpeedSettings,
@@ -888,7 +891,9 @@ export default function DirectPlayerPage() {
         const queryParams = new URLSearchParams({
           itemId: item?.Id ?? "",
           audioIndex: String(index),
-          subtitleIndex: String(currentSubtitleIndex),
+          // A local (client-downloaded) sub only exists in the dying mpv
+          // instance — the server must be asked for "none" (-1) instead.
+          subtitleIndex: String(toServerSubtitleIndex(currentSubtitleIndex)),
           mediaSourceId: stream?.mediaSource?.Id ?? "",
           bitrateValue: bitrateValue?.toString() ?? "",
           playbackPosition: msToTicks(progress.get()).toString(),
@@ -954,7 +959,9 @@ export default function DirectPlayerPage() {
       const queryParams = new URLSearchParams({
         itemId: item?.Id ?? "",
         audioIndex: params.audioIndex ?? String(currentAudioIndex ?? ""),
-        subtitleIndex: params.subtitleIndex ?? String(currentSubtitleIndex),
+        subtitleIndex:
+          params.subtitleIndex ??
+          String(toServerSubtitleIndex(currentSubtitleIndex)),
         mediaSourceId: stream?.mediaSource?.Id ?? "",
         bitrateValue: bitrateValue?.toString() ?? "",
         playbackPosition: msToTicks(progress.get()).toString(),

components/video-player/controls/contexts/VideoContext.tsx

@@ -126,10 +126,17 @@ export const VideoProvider: React.FC<{ children: ReactNode }> = ({
     audioIndex?: string;
     subtitleIndex?: string;
   }) => {
+    // The URL param can hold a local-sub sentinel (selected via setParams) that
+    // only exists in the dying player — the server must get "none" (-1) instead.
+    // NaN (missing/blank param) fails the comparison and passes through as-is.
+    const fallbackSubtitleIndex =
+      Number.parseInt(subtitleIndex, 10) <= LOCAL_SUBTITLE_INDEX_START
+        ? "-1"
+        : subtitleIndex;
     const queryParams = new URLSearchParams({
       itemId: itemId ?? "",
       audioIndex: params.audioIndex ?? audioIndex,
-      subtitleIndex: params.subtitleIndex ?? subtitleIndex,
+      subtitleIndex: params.subtitleIndex ?? fallbackSubtitleIndex,
       mediaSourceId: mediaSource?.Id ?? "",
       bitrateValue: bitrateValue,
       playbackPosition: playbackPosition,

components/video-player/controls/types.ts

@@ -36,4 +36,12 @@ type Track = {
  */
 export const LOCAL_SUBTITLE_INDEX_START = -100;
 
+/**
+ * Map a client-side subtitle index to what the Jellyfin stream API understands.
+ * Local sentinel indexes have no matching MediaStream on the server, which
+ * expects -1 ("no subtitles") when re-negotiating a stream.
+ */
+export const toServerSubtitleIndex = (index: number): number =>
+  index <= LOCAL_SUBTITLE_INDEX_START ? -1 : index;
+
 export type { EmbeddedSubtitle, ExternalSubtitle, Track, TranscodedSubtitle };