diff --git a/RELEASENOTES.md b/RELEASENOTES.md
index c22e1e648d..e99fd84e74 100644
--- a/RELEASENOTES.md
+++ b/RELEASENOTES.md
@@ -50,6 +50,14 @@
         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.
 *   Ad playback:
     *   Support changing ad break positions in the player logic
         ([#5067](https://github.com/google/ExoPlayer/issues/5067).
diff --git a/library/extractor/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java b/library/extractor/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java
index e3e5f27090..0ec5bd48ed 100644
--- a/library/extractor/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java
+++ b/library/extractor/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java
@@ -556,7 +556,7 @@ public class FragmentedMp4Extractor implements Extractor {
   }
 
   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) {
@@ -703,7 +703,8 @@ public class FragmentedMp4Extractor implements Extractor {
 
   private static void parseMoof(
       ContainerAtom moof,
-      SparseArray<TrackBundle> trackBundleArray,
+      SparseArray<TrackBundle> trackBundles,
+      boolean haveSideloadedTrack,
       @Flags int flags,
       byte[] extendedTypeScratch)
       throws ParserException {
@@ -712,7 +713,7 @@ public class FragmentedMp4Extractor implements Extractor {
       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);
       }
     }
   }
@@ -720,12 +721,13 @@ public class FragmentedMp4Extractor implements Extractor {
   /** Parses a traf atom (defined in 14496-12). */
   private static void parseTraf(
       ContainerAtom traf,
-      SparseArray<TrackBundle> trackBundleArray,
+      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;
     }
@@ -883,17 +885,21 @@ public class FragmentedMp4Extractor implements Extractor {
    *
    * @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;
     }
@@ -929,17 +935,6 @@ public class FragmentedMp4Extractor implements Extractor {
     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).
    *