shadows/framework/src/main/java/org/robolectric/shadows/ShadowMediaMuxer.java
@Implementation
  protected static int nativeAddTrack(
      long nativeObject, @NonNull String[] keys, @NonNull Object[] values) {
    AtomicInteger nextTrackIndex = nextTrackIndices.get(nativeObject);
    if (nextTrackIndex == null) {
      throw new IllegalStateException("No next track index configured for key: " + nativeObject);
    }

    return nextTrackIndex.getAndIncrement();
  }
@Implementation
  protected static int nativeAddTrack(
      long nativeObject, @NonNull String[] keys, @NonNull Object[] values) {
    AtomicInteger nextTrackIndex = nextTrackIndices.get(nativeObject);
    if (nextTrackIndex == null) {
      throw new IllegalStateException("No next track index configured for key: " + nativeObject);
    }

    return nextTrackIndex.getAndIncrement();
  }
Returns an incremented track id for the associated muxer.