refactor mpv state mapping into mpv-state helper

src/core/services/mpv-state.ts

@@ -0,0 +1,25 @@
+export type MpvTrackProperty = {
+  type?: string;
+  id?: number;
+  selected?: boolean;
+  "ff-index"?: number;
+};
+
+export function resolveCurrentAudioStreamIndex(
+  tracks: Array<MpvTrackProperty> | null | undefined,
+  currentAudioTrackId: number | null,
+): number | null {
+  if (!Array.isArray(tracks)) {
+    return null;
+  }
+
+  const audioTracks = tracks.filter((track) => track.type === "audio");
+  const activeTrack =
+    audioTracks.find((track) => track.id === currentAudioTrackId) ||
+    audioTracks.find((track) => track.selected === true);
+
+  const ffIndex = activeTrack?.["ff-index"];
+  return typeof ffIndex === "number" && Number.isInteger(ffIndex) && ffIndex >= 0
+    ? ffIndex
+    : null;
+}