Fix issue where a trun atom could be associated with the wrong track

Note that this removes a workaround for malformed content, in which the
track_ID is set incorrectly. It's unclear there was sufficient reason to
implement that workaround, and so it's preferable to remove it, rather
than implementing the concept of unrecognized tracks, which would be
needed to keep it and to also fix this issue.

Issue: #9056
PiperOrigin-RevId: 379506261

RELEASENOTES.md

@@ -11,6 +11,14 @@
         passthrough capability from API 29 onwards, instead of using the HDMI
         audio plug intent
         ([#6500](https://github.com/google/ExoPlayer/pull/6500)).
+*   Extractors:
+    *   Fix issue where a `trun` atom could be associated with the wrong track
+        in an FMP4 stream
+        ([#9056](https://github.com/google/ExoPlayer/pull/9056)). The fix
+        removes a previous workaround to handle content in which the `track_ID`
+        is set incorrectly
+        ([#4083](https://github.com/google/ExoPlayer/issues/4083)). Such content
+        is malformed and should be re-encoded.
 *   UI:
     *   Add `PendingIntent.FLAG_IMMUTABLE` flag when creating a broadcast intent
         in `PlayerNotificationManager`. This is required to avoid an error on

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java

@@ -557,7 +557,7 @@ private DefaultSampleValues getDefaultSampleValues(
   }
 
   private void onMoofContainerAtomRead(ContainerAtom moof) throws ParserException {
-    parseMoof(moof, trackBundles, flags, scratchBytes);
+    parseMoof(moof, trackBundles, sideloadedTrack != null, flags, scratchBytes);
 
     @Nullable DrmInitData drmInitData = getDrmInitDataFromAtoms(moof.leafChildren);
     if (drmInitData != null) {
@@ -699,25 +699,27 @@ private static long parseMehd(ParsableByteArray mehd) {
     return version == 0 ? mehd.readUnsignedInt() : mehd.readUnsignedLongToLong();
   }
 
-  private static void parseMoof(ContainerAtom moof, SparseArray<TrackBundle> trackBundleArray,
+  private static void parseMoof(ContainerAtom moof, SparseArray<TrackBundle> trackBundles,
+      boolean haveSideloadedTrack,
       @Flags int flags, byte[] extendedTypeScratch) throws ParserException {
     int moofContainerChildrenSize = moof.containerChildren.size();
     for (int i = 0; i < moofContainerChildrenSize; i++) {
       Atom.ContainerAtom child = moof.containerChildren.get(i);
       // TODO: Support multiple traf boxes per track in a single moof.
       if (child.type == Atom.TYPE_traf) {
-        parseTraf(child, trackBundleArray, flags, extendedTypeScratch);
+        parseTraf(child, trackBundles, haveSideloadedTrack, flags, extendedTypeScratch);
       }
     }
   }
 
   /**
    * Parses a traf atom (defined in 14496-12).
    */
-  private static void parseTraf(ContainerAtom traf, SparseArray<TrackBundle> trackBundleArray,
+  private static void parseTraf(ContainerAtom traf, SparseArray<TrackBundle> trackBundles,
+      boolean haveSideloadedTrack,
       @Flags int flags, byte[] extendedTypeScratch) throws ParserException {
     LeafAtom tfhd = checkNotNull(traf.getLeafAtomOfType(Atom.TYPE_tfhd));
-    @Nullable TrackBundle trackBundle = parseTfhd(tfhd.data, trackBundleArray);
+    @Nullable TrackBundle trackBundle = parseTfhd(tfhd.data, trackBundles, haveSideloadedTrack);
     if (trackBundle == null) {
       return;
     }
@@ -874,17 +876,21 @@ private static void parseSaio(ParsableByteArray saio, TrackFragment out) throws
    *
    * @param tfhd The tfhd atom to decode.
    * @param trackBundles The track bundles, one of which corresponds to the tfhd atom being parsed.
+   * @param haveSideloadedTrack Whether {@code trackBundles} contains a single bundle corresponding
+   *     to a side-loaded track.
    * @return The {@link TrackBundle} to which the {@link TrackFragment} belongs, or null if the tfhd
    *     does not refer to any {@link TrackBundle}.
    */
   @Nullable
   private static TrackBundle parseTfhd(
-      ParsableByteArray tfhd, SparseArray<TrackBundle> trackBundles) {
+      ParsableByteArray tfhd, SparseArray<TrackBundle> trackBundles, boolean haveSideloadedTrack) {
     tfhd.setPosition(Atom.HEADER_SIZE);
     int fullAtom = tfhd.readInt();
     int atomFlags = Atom.parseFullAtomFlags(fullAtom);
     int trackId = tfhd.readInt();
-    @Nullable TrackBundle trackBundle = getTrackBundle(trackBundles, trackId);
+    @Nullable
+    TrackBundle trackBundle =
+        haveSideloadedTrack ? trackBundles.valueAt(0) : trackBundles.get(trackId);
     if (trackBundle == null) {
       return null;
     }
@@ -916,17 +922,6 @@ private static TrackBundle parseTfhd(
     return trackBundle;
   }
 
-  private static @Nullable TrackBundle getTrackBundle(
-      SparseArray<TrackBundle> trackBundles, int trackId) {
-    if (trackBundles.size() == 1) {
-      // Ignore track id if there is only one track. This is either because we have a side-loaded
-      // track or to cope with non-matching track indices (see
-      // https://github.com/google/ExoPlayer/issues/4083).
-      return trackBundles.valueAt(/* index= */ 0);
-    }
-    return trackBundles.get(trackId);
-  }
-
   /**
    * Parses a tfdt atom (defined in 14496-12).
    *