Report initial discontinuity for DASH periods that require preroll

DASH periods don't have to start at the beginning of a segment. In
these cases, they should report an initial discontinuity to let the
player know it needs to expect preroll data (e.g. to flush renderers)

This information is only available in the ChunkSampleStream after
loading the initialization data, so we need to check the sample
streams and tell them to only report discontinuities at the very
beginning of playback. All other position resets are triggered by
the player itself and don't need this method.

Issue: #1440
PiperOrigin-RevId: 668831563

RELEASENOTES.md

@@ -101,6 +101,9 @@
 *   Cronet Extension:
 *   RTMP Extension:
 *   HLS Extension:
+*   DASH Extension:
+    *   Add support for periods starting in the middle of a segment
+        ([#1440](https://github.com/androidx/media/issues/1440)).
 *   Smooth Streaming Extension:
 *   RTSP Extension:
 *   Decoder Extensions (FFmpeg, VP9, AV1, etc.):

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/chunk/ChunkSampleStream.java

@@ -22,6 +22,7 @@
 import androidx.annotation.Nullable;
 import androidx.media3.common.C;
 import androidx.media3.common.Format;
+import androidx.media3.common.MimeTypes;
 import androidx.media3.common.util.Assertions;
 import androidx.media3.common.util.Log;
 import androidx.media3.common.util.UnstableApi;
@@ -95,6 +96,8 @@ public interface ReleaseCallback<T extends ChunkSource> {
   private long lastSeekPositionUs;
   private int nextNotifyPrimaryFormatMediaChunkIndex;
   @Nullable private BaseMediaChunk canceledMediaChunk;
+  private boolean canReportInitialDiscontinuity;
+  private boolean hasInitialDiscontinuity;
 
   /* package */ boolean loadingFinished;
 
@@ -114,6 +117,8 @@ public interface ReleaseCallback<T extends ChunkSource> {
    * @param loadErrorHandlingPolicy The {@link LoadErrorHandlingPolicy}.
    * @param mediaSourceEventDispatcher A dispatcher to notify of {@link MediaSourceEventListener}
    *     events.
+   * @param canReportInitialDiscontinuity Whether the stream can report an initial discontinuity if
+   *     the first chunk can't start at the beginning and needs to preroll data.
    */
   public ChunkSampleStream(
       @C.TrackType int primaryTrackType,
@@ -126,14 +131,16 @@ public ChunkSampleStream(
       DrmSessionManager drmSessionManager,
       DrmSessionEventListener.EventDispatcher drmEventDispatcher,
       LoadErrorHandlingPolicy loadErrorHandlingPolicy,
-      MediaSourceEventListener.EventDispatcher mediaSourceEventDispatcher) {
+      MediaSourceEventListener.EventDispatcher mediaSourceEventDispatcher,
+      boolean canReportInitialDiscontinuity) {
     this.primaryTrackType = primaryTrackType;
     this.embeddedTrackTypes = embeddedTrackTypes == null ? new int[0] : embeddedTrackTypes;
     this.embeddedTrackFormats = embeddedTrackFormats == null ? new Format[0] : embeddedTrackFormats;
     this.chunkSource = chunkSource;
     this.callback = callback;
     this.mediaSourceEventDispatcher = mediaSourceEventDispatcher;
     this.loadErrorHandlingPolicy = loadErrorHandlingPolicy;
+    this.canReportInitialDiscontinuity = canReportInitialDiscontinuity;
     loader = new Loader("ChunkSampleStream");
     nextChunkHolder = new ChunkHolder();
     mediaChunks = new ArrayList<>();
@@ -258,6 +265,7 @@ public long getAdjustedSeekPositionUs(long positionUs, SeekParameters seekParame
    */
   public void seekToUs(long positionUs) {
     lastSeekPositionUs = positionUs;
+    canReportInitialDiscontinuity = false;
     if (isPendingReset()) {
       // A reset is already pending. We only need to update its position.
       pendingResetPositionUs = positionUs;
@@ -600,12 +608,22 @@ public boolean continueLoading(LoadingInfo loadingInfo) {
         // seeking to a chunk boundary then we want the queue to pass through all of the samples in
         // the chunk. Doing this ensures we'll always output the keyframe at the start of the chunk,
         // even if its timestamp is slightly earlier than the advertised chunk start time.
-        if (mediaChunk.startTimeUs != pendingResetPositionUs) {
+        if (mediaChunk.startTimeUs < pendingResetPositionUs) {
           primarySampleQueue.setStartTimeUs(pendingResetPositionUs);
           for (SampleQueue embeddedSampleQueue : embeddedSampleQueues) {
             embeddedSampleQueue.setStartTimeUs(pendingResetPositionUs);
           }
+          if (canReportInitialDiscontinuity) {
+            // Only report it as discontinuity if the SampleQueue can't skip the samples directly.
+            boolean sampleQueueCanSkipSamples =
+                MimeTypes.allSamplesAreSyncSamples(
+                    mediaChunk.trackFormat.sampleMimeType, mediaChunk.trackFormat.codecs);
+            hasInitialDiscontinuity = !sampleQueueCanSkipSamples;
+          }
         }
+        // Once we started loading the first media chunk, no more initial discontinuities can be
+        // reported.
+        canReportInitialDiscontinuity = false;
         pendingResetPositionUs = C.TIME_UNSET;
       }
       mediaChunk.init(chunkOutput);
@@ -670,6 +688,19 @@ && haveReadFromMediaChunk(/* mediaChunkIndex= */ mediaChunks.size() - 1)) {
     }
   }
 
+  /**
+   * Consumes a pending initial discontinuity.
+   *
+   * @return Whether the stream had an initial discontinuity.
+   */
+  public boolean consumeInitialDiscontinuity() {
+    try {
+      return hasInitialDiscontinuity;
+    } finally {
+      hasInitialDiscontinuity = false;
+    }
+  }
+
   private void discardUpstream(int preferredQueueSize) {
     Assertions.checkState(!loader.isLoading());
 

libraries/exoplayer_dash/src/main/java/androidx/media3/exoplayer/dash/DashMediaPeriod.java

@@ -114,6 +114,8 @@
   private DashManifest manifest;
   private int periodIndex;
   private List<EventStream> eventStreams;
+  private boolean canReportInitialDiscontinuity;
+  private long initialStartTimeUs;
 
   public DashMediaPeriod(
       int id,
@@ -149,6 +151,7 @@ public DashMediaPeriod(
     this.allocator = allocator;
     this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
     this.playerId = playerId;
+    this.canReportInitialDiscontinuity = true;
     playerEmsgHandler = new PlayerEmsgHandler(manifest, playerEmsgCallback, allocator);
     sampleStreams = newSampleStreamArray(0);
     eventSampleStreams = new EventSampleStream[0];
@@ -305,6 +308,10 @@ public long selectTracks(
         compositeSequenceableLoaderFactory.create(
             sampleStreamList,
             Lists.transform(sampleStreamList, s -> ImmutableList.of(s.primaryTrackType)));
+    if (canReportInitialDiscontinuity) {
+      canReportInitialDiscontinuity = false;
+      initialStartTimeUs = positionUs;
+    }
     return positionUs;
   }
 
@@ -337,6 +344,11 @@ public long getNextLoadPositionUs() {
 
   @Override
   public long readDiscontinuity() {
+    for (ChunkSampleStream<DashChunkSource> sampleStream : sampleStreams) {
+      if (sampleStream.consumeInitialDiscontinuity()) {
+        return initialStartTimeUs;
+      }
+    }
     return C.TIME_UNSET;
   }
 
@@ -824,7 +836,8 @@ private ChunkSampleStream<DashChunkSource> buildSampleStream(
             drmSessionManager,
             drmEventDispatcher,
             loadErrorHandlingPolicy,
-            mediaSourceEventDispatcher);
+            mediaSourceEventDispatcher,
+            canReportInitialDiscontinuity);
     synchronized (this) {
       // The map is also accessed on the loading thread so synchronize access.
       trackEmsgHandlerBySampleStream.put(stream, trackPlayerEmsgHandler);

libraries/exoplayer_dash/src/test/java/androidx/media3/exoplayer/dash/e2etest/DashPlaybackTest.java

@@ -440,4 +440,27 @@ public void playVideo_usingWithinGopSampleDependencies_withSeekAfterEoS() throws
     // TODO: b/352276461 - The last frame might not be rendered. When the bug is fixed,
     //  assert on the full playback dump.
   }
+
+  @Test
+  public void multiPeriod_withOffsetInSegment() throws Exception {
+    Context applicationContext = ApplicationProvider.getApplicationContext();
+    CapturingRenderersFactory capturingRenderersFactory =
+        new CapturingRenderersFactory(applicationContext);
+    ExoPlayer player =
+        new ExoPlayer.Builder(applicationContext, capturingRenderersFactory)
+            .setClock(new FakeClock(/* isAutoAdvancing= */ true))
+            .build();
+    player.setVideoSurface(new Surface(new SurfaceTexture(/* texName= */ 1)));
+    PlaybackOutput playbackOutput = PlaybackOutput.register(player, capturingRenderersFactory);
+
+    player.setMediaItem(
+        MediaItem.fromUri("asset:///media/dash/multi-period-with-offset/sample.mpd"));
+    player.prepare();
+    player.play();
+    TestPlayerRunHelper.runUntilPlaybackState(player, Player.STATE_ENDED);
+    player.release();
+
+    DumpFileAsserts.assertOutput(
+        applicationContext, playbackOutput, "playbackdumps/dash/multi-period-with-offset.dump");
+  }
 }

libraries/exoplayer_smoothstreaming/src/main/java/androidx/media3/exoplayer/smoothstreaming/SsMediaPeriod.java

@@ -264,7 +264,8 @@ private ChunkSampleStream<SsChunkSource> buildSampleStream(
         drmSessionManager,
         drmEventDispatcher,
         loadErrorHandlingPolicy,
-        mediaSourceEventDispatcher);
+        mediaSourceEventDispatcher,
+        /* canReportInitialDiscontinuity= */ false);
   }
 
   private static TrackGroupArray buildTrackGroups(

libraries/test_data/src/test/assets/media/dash/multi-period-with-offset/sample.mpd

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" type="static" mediaPresentationDuration="PT1.0010000467300415S">
+  <Period id='0' duration='PT0.5S'>
+    <AdaptationSet id="1" contentType="video" width="1080" height="720" frameRate="30000/1001" subsegmentAlignment="true" par="3:2">
+      <Representation id="1" bandwidth="721967" codecs="avc1.64001f" mimeType="video/mp4" sar="1:1">
+        <BaseURL>sample.video.mp4</BaseURL>
+        <SegmentBase indexRange="862-905" timescale="30000">
+          <Initialization range="0-861"/>
+        </SegmentBase>
+      </Representation>
+    </AdaptationSet>
+  </Period>
+  <Period id='1'>
+      <AdaptationSet id="1" contentType="video" width="1080" height="720" frameRate="30000/1001" subsegmentAlignment="true" par="3:2">
+        <Representation id="1" bandwidth="721967" codecs="avc1.64001f" mimeType="video/mp4" sar="1:1">
+          <BaseURL>sample.video.mp4</BaseURL>
+          <SegmentBase indexRange="862-905" timescale="30000" presentationTimeOffset="15000">
+            <Initialization range="0-861"/>
+          </SegmentBase>
+        </Representation>
+      </AdaptationSet>
+    </Period>
+</MPD>