Bugfix: Handle seekhead for cues on mkv files.

Author: KingLucius

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/e2etest/MkvPlaybackTest.java

@@ -57,7 +57,8 @@ public static ImmutableList<String> mediaSamples() {
         "sample_with_overlapping_srt.mkv",
         "sample_with_vtt_subtitles.mkv",
         "sample_with_null_terminated_vtt_subtitles.mkv",
-        "sample_with_vobsub.mkv");
+        "sample_with_vobsub.mkv",
+        "sample_recursive_seekhead.mkv");
   }
 
   @ParameterizedRobolectricTestRunner.Parameter public String inputFile;

libraries/extractor/src/main/java/androidx/media3/extractor/mkv/MatroskaExtractor.java

@@ -456,6 +456,9 @@ public static ExtractorsFactory newFactory(SubtitleParser.Factory subtitleParser
 
   // Cue related elements.
   private boolean seekForCues;
+  private boolean seekForSeekContent;
+  private long seekPositionAfterSeekingForHead = C.INDEX_UNSET;
+  private long seekHeadContentPosition = C.INDEX_UNSET;
   private long cuesContentPosition = C.INDEX_UNSET;
   private long seekPositionAfterBuildingCues = C.INDEX_UNSET;
   private long clusterTimecodeUs = C.TIME_UNSET;
@@ -764,6 +767,10 @@ protected void startMasterElement(int id, long contentPosition, long contentSize
           if (seekForCuesEnabled && cuesContentPosition != C.INDEX_UNSET) {
             // We know where the Cues element is located. Seek to request it.
             seekForCues = true;
+          } else if (seekForCuesEnabled && seekHeadContentPosition != C.INDEX_UNSET) {
+            // We do not know where the cues are located, however we have a seek-head entry
+            // we have not yet visited
+            seekForSeekContent = true;
           } else {
             // We don't know where the Cues element is located. It's most likely omitted. Allow
             // playback, but disable seeking.
@@ -816,9 +823,16 @@ protected void endMasterElement(int id) throws ParserException {
         if (seekEntryId == UNSET_ENTRY_ID || seekEntryPosition == C.INDEX_UNSET) {
           throw ParserException.createForMalformedContainer(
               "Mandatory element SeekID or SeekPosition not found", /* cause= */ null);
-        }
-        if (seekEntryId == ID_CUES) {
+        } else if (seekEntryId == ID_SEEK_HEAD) {
+          seekHeadContentPosition = seekEntryPosition;
+        } else if (seekEntryId == ID_CUES) {
           cuesContentPosition = seekEntryPosition;
+
+          // We are currently seeking from the seek-head, so we seek again to get to the cues
+          // instead of waiting for the cluster
+          if (seekForCuesEnabled && seekPositionAfterSeekingForHead != C.INDEX_UNSET) {
+            seekForCues = true;
+          }
         }
         break;
       case ID_CUES:
@@ -1936,6 +1950,13 @@ private SeekMap buildSeekMap(
    * @return Whether the seek position was updated.
    */
   private boolean maybeSeekForCues(PositionHolder seekPosition, long currentPosition) {
+    if (seekForSeekContent) {
+      seekPositionAfterSeekingForHead = currentPosition;
+      seekPosition.position = seekHeadContentPosition;
+      seekForSeekContent = false;
+      return true;
+    }
+
     if (seekForCues) {
       seekPositionAfterBuildingCues = currentPosition;
       seekPosition.position = cuesContentPosition;
@@ -1949,6 +1970,16 @@ private boolean maybeSeekForCues(PositionHolder seekPosition, long currentPositi
       seekPositionAfterBuildingCues = C.INDEX_UNSET;
       return true;
     }
+
+    // After we have seeked back from seekPositionAfterBuildingCues seek back again to parse the
+    // rest of the file. This ends the double jump that is preformed when the beginning metadata
+    // only contains a ID_SEEK_HEAD without a ID_CUES.
+    if (sentSeekMap && seekPositionAfterSeekingForHead != C.INDEX_UNSET) {
+      seekPosition.position = seekPositionAfterSeekingForHead;
+      seekPositionAfterSeekingForHead = C.INDEX_UNSET;
+      return true;
+    }
+
     return false;
   }
 

libraries/extractor/src/test/java/androidx/media3/extractor/mkv/MatroskaExtractorTest.java

@@ -140,6 +140,17 @@ public void mkvSample_withNullTerminatedVttSubtitles() throws Exception {
         simulationConfig);
   }
 
+  // https://github.com/androidx/media/issues/1143
+  @Test
+  public void mkvSample_withRecursiveSeekHead() throws Exception {
+    ExtractorAsserts.assertBehavior(
+        getExtractorFactory(subtitlesParsedDuringExtraction),
+        "media/mkv/sample_recursive_seekhead.mkv",
+        getAssertionConfigWithPrefix(
+            "media/mkv/sample_recursive_seekhead.mkv", subtitlesParsedDuringExtraction),
+        simulationConfig);
+  }
+
   @Test
   public void mkvSample_withVorbisAudio() throws Exception {
     ExtractorAsserts.assertBehavior(