Split MediaViewModel into multiple files

src/state/observeTrackReference.ts

@@ -0,0 +1,28 @@
+/*
+Copyright 2023, 2024 New Vector Ltd.
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  observeParticipantMedia,
+  type TrackReference,
+} from "@livekit/components-core";
+import { type Participant, type Track } from "livekit-client";
+import { distinctUntilChanged, map, type Observable } from "rxjs";
+
+/**
+ * Reactively reads a participant's track reference for a given media source.
+ */
+export function observeTrackReference$(
+  participant: Participant,
+  source: Track.Source,
+): Observable<TrackReference | undefined> {
+  return observeParticipantMedia(participant).pipe(
+    map(() => participant.getTrackPublication(source)),
+    distinctUntilChanged(),
+    map((publication) => publication && { participant, publication, source }),
+  );
+}