HLS: Allow audio variants to initialize the timestamp adjuster

This makes HLS playback less liable to become stuck if discontinuity
tags are inserted at different times across media playlists.

Issue: #8700
Issue: #8372
PiperOrigin-RevId: 362903428

RELEASENOTES.md

@@ -24,14 +24,19 @@
     *   `DebugTextViewHelper` moved from `ui` package to `util` package.
     *   Spherical UI components moved from `video.spherical` package to
         `ui.spherical` package, and made package private.
-*   Core
+*   Core:
     *   Move `getRendererCount` and `getRendererType` methods from `Player` to
         `ExoPlayer`.
     *   Reset playback speed when live playback speed control becomes unused
         ([#8664](https://github.com/google/ExoPlayer/issues/8664)).
     *   Fix playback position issue when re-preparing playback after a
         BehindLiveWindowException
         ([#8675](https://github.com/google/ExoPlayer/issues/8675)).
+*   HLS:
+    *   Fix issue that could cause playback to become stuck if corresponding
+        `EXT-X-DISCONTINUITY` tags in different media playlists occur at
+        different positions in time
+        ([#8372](https://github.com/google/ExoPlayer/issues/8372)).
 *   Remove deprecated symbols:
     *   Remove `Player.DefaultEventListener`. Use `Player.EventListener`
         instead.

library/common/src/main/java/com/google/android/exoplayer2/util/TimestampAdjuster.java

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2.util;
 
+import androidx.annotation.GuardedBy;
 import com.google.android.exoplayer2.C;
 
 /**
@@ -35,34 +36,73 @@ public final class TimestampAdjuster {
    */
   private static final long MAX_PTS_PLUS_ONE = 0x200000000L;
 
+  @GuardedBy("this")
+  private boolean sharedInitializationStarted;
+
+  @GuardedBy("this")
   private long firstSampleTimestampUs;
+
+  @GuardedBy("this")
   private long timestampOffsetUs;
 
-  // Volatile to allow isInitialized to be called on a different thread to adjustSampleTimestamp.
-  private volatile long lastSampleTimestampUs;
+  @GuardedBy("this")
+  private long lastSampleTimestampUs;
 
   /**
-   * @param firstSampleTimestampUs See {@link #setFirstSampleTimestampUs(long)}.
+   * @param firstSampleTimestampUs The desired value of the first adjusted sample timestamp in
+   *     microseconds, or {@link #DO_NOT_OFFSET} if timestamps should not be offset.
    */
   public TimestampAdjuster(long firstSampleTimestampUs) {
+    this.firstSampleTimestampUs = firstSampleTimestampUs;
     lastSampleTimestampUs = C.TIME_UNSET;
-    setFirstSampleTimestampUs(firstSampleTimestampUs);
   }
 
   /**
-   * Sets the desired result of the first call to {@link #adjustSampleTimestamp(long)}. Can only be
-   * called before any timestamps have been adjusted.
+   * For shared timestamp adjusters, performs necessary initialization actions for a caller.
    *
-   * @param firstSampleTimestampUs The first adjusted sample timestamp in microseconds, or
-   *     {@link #DO_NOT_OFFSET} if presentation timestamps should not be offset.
+   * <ul>
+   *   <li>If the adjuster does not yet have a target {@link #getFirstSampleTimestampUs first sample
+   *       timestamp} and if {@code canInitialize} is {@code true}, then initialization is started
+   *       by setting the target first sample timestamp to {@code firstSampleTimestampUs}. The call
+   *       returns, allowing the caller to proceed. Initialization completes when a caller adjusts
+   *       the first timestamp.
+   *   <li>If {@code canInitialize} is {@code true} and the adjuster already has a target {@link
+   *       #getFirstSampleTimestampUs first sample timestamp}, then the call returns to allow the
+   *       caller to proceed only if {@code firstSampleTimestampUs} is equal to the target. This
+   *       ensures a caller that's previously started initialization can continue to proceed. It
+   *       also allows other callers with the same {@code firstSampleTimestampUs} to proceed, since
+   *       in this case it doesn't matter which caller adjusts the first timestamp to complete
+   *       initialization.
+   *   <li>If {@code canInitialize} is {@code false} or if {@code firstSampleTimestampUs} differs
+   *       from the target {@link #getFirstSampleTimestampUs first sample timestamp}, then the call
+   *       blocks until initialization completes. If initialization has already been completed the
+   *       call returns immediately.
+   * </ul>
+   *
+   * @param canInitialize Whether the caller is able to initialize the adjuster, if needed.
+   * @param startTimeUs The desired first sample timestamp of the caller, in microseconds. Only used
+   *     if {@code canInitialize} is {@code true}.
+   * @throws InterruptedException If the thread is interrupted whilst blocked waiting for
+   *     initialization to complete.
    */
-  public synchronized void setFirstSampleTimestampUs(long firstSampleTimestampUs) {
-    Assertions.checkState(lastSampleTimestampUs == C.TIME_UNSET);
-    this.firstSampleTimestampUs = firstSampleTimestampUs;
+  public synchronized void sharedInitializeOrWait(boolean canInitialize, long startTimeUs)
+      throws InterruptedException {
+    if (canInitialize && !sharedInitializationStarted) {
+      firstSampleTimestampUs = startTimeUs;
+      sharedInitializationStarted = true;
+    }
+    if (!canInitialize || startTimeUs != firstSampleTimestampUs) {
+      while (lastSampleTimestampUs == C.TIME_UNSET) {
+        wait();
+      }
+    }
   }
 
-  /** Returns the last value passed to {@link #setFirstSampleTimestampUs(long)}. */
-  public long getFirstSampleTimestampUs() {
+  /**
+   * Returns the value of the first adjusted sample timestamp in microseconds, or {@link
+   * #DO_NOT_OFFSET} if timestamps will not be offset.
+   */
+  public synchronized long getFirstSampleTimestampUs() {
     return firstSampleTimestampUs;
   }
 
@@ -72,32 +112,37 @@ public long getFirstSampleTimestampUs() {
    * #getFirstSampleTimestampUs()}. If this value is {@link #DO_NOT_OFFSET}, returns {@link
    * C#TIME_UNSET}.
    */
-  public long getLastAdjustedTimestampUs() {
+  public synchronized long getLastAdjustedTimestampUs() {
     return lastSampleTimestampUs != C.TIME_UNSET
         ? (lastSampleTimestampUs + timestampOffsetUs)
         : firstSampleTimestampUs != DO_NOT_OFFSET ? firstSampleTimestampUs : C.TIME_UNSET;
   }
 
   /**
-   * Returns the offset between the input of {@link #adjustSampleTimestamp(long)} and its output.
-   * If {@link #DO_NOT_OFFSET} was provided to the constructor, 0 is returned. If the timestamp
+   * Returns the offset between the input of {@link #adjustSampleTimestamp(long)} and its output. If
+   * {@link #DO_NOT_OFFSET} was provided to the constructor, 0 is returned. If the timestamp
    * adjuster is yet not initialized, {@link C#TIME_UNSET} is returned.
    *
-   * @return The offset between {@link #adjustSampleTimestamp(long)}'s input and output.
-   *     {@link C#TIME_UNSET} if the adjuster is not yet initialized and 0 if timestamps should not
-   *     be offset.
+   * @return The offset between {@link #adjustSampleTimestamp(long)}'s input and output. {@link
+   *     C#TIME_UNSET} if the adjuster is not yet initialized and 0 if timestamps should not be
+   *     offset.
    */
-  public long getTimestampOffsetUs() {
+  public synchronized long getTimestampOffsetUs() {
     return firstSampleTimestampUs == DO_NOT_OFFSET
         ? 0
         : lastSampleTimestampUs == C.TIME_UNSET ? C.TIME_UNSET : timestampOffsetUs;
   }
 
   /**
    * Resets the instance to its initial state.
+   *
+   * @param firstSampleTimestampUs The desired value of the first adjusted sample timestamp after
+   *     this reset, in microseconds, or {@link #DO_NOT_OFFSET} if timestamps should not be offset.
    */
-  public void reset() {
+  public synchronized void reset(long firstSampleTimestampUs) {
+    this.firstSampleTimestampUs = firstSampleTimestampUs;
     lastSampleTimestampUs = C.TIME_UNSET;
+    sharedInitializationStarted = false;
   }
 
   /**
@@ -106,7 +151,7 @@ public void reset() {
    * @param pts90Khz A 90 kHz clock MPEG-2 TS presentation timestamp.
    * @return The adjusted timestamp in microseconds.
    */
-  public long adjustTsTimestamp(long pts90Khz) {
+  public synchronized long adjustTsTimestamp(long pts90Khz) {
     if (pts90Khz == C.TIME_UNSET) {
       return C.TIME_UNSET;
     }
@@ -131,7 +176,7 @@ public long adjustTsTimestamp(long pts90Khz) {
    * @param timeUs The timestamp to adjust in microseconds.
    * @return The adjusted timestamp in microseconds.
    */
-  public long adjustSampleTimestamp(long timeUs) {
+  public synchronized long adjustSampleTimestamp(long timeUs) {
     if (timeUs == C.TIME_UNSET) {
       return C.TIME_UNSET;
     }
@@ -143,26 +188,13 @@ public long adjustSampleTimestamp(long timeUs) {
         // Calculate the timestamp offset.
         timestampOffsetUs = firstSampleTimestampUs - timeUs;
       }
-      synchronized (this) {
-        lastSampleTimestampUs = timeUs;
-        // Notify threads waiting for this adjuster to be initialized.
-        notifyAll();
-      }
+      lastSampleTimestampUs = timeUs;
+      // Notify threads waiting for this adjuster to be initialized.
+      notifyAll();
     }
     return timeUs + timestampOffsetUs;
   }
 
-  /**
-   * Blocks the calling thread until this adjuster is initialized.
-   *
-   * @throws InterruptedException If the thread was interrupted.
-   */
-  public synchronized void waitUntilInitialized() throws InterruptedException {
-    while (lastSampleTimestampUs == C.TIME_UNSET) {
-      wait();
-    }
-  }
-
   /**
    * Converts a 90 kHz clock timestamp to a timestamp in microseconds.
    *

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/ts/PsExtractor.java

@@ -144,8 +144,7 @@ public void seek(long position, long timeUs) {
       // we have to set the first sample timestamp manually.
       // - If the timestamp adjuster has its timestamp set manually before, and now we seek to a
       // different position, we need to set the first sample timestamp manually again.
-      timestampAdjuster.reset();
-      timestampAdjuster.setFirstSampleTimestampUs(timeUs);
+      timestampAdjuster.reset(timeUs);
     }
 
     if (psBinarySearchSeeker != null) {

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/ts/TsExtractor.java

@@ -268,8 +268,7 @@ public void seek(long position, long timeUs) {
         // sample timestamp for that track manually.
         // - If the timestamp adjuster has its timestamp set manually before, and now we seek to a
         // different position, we need to set the first sample timestamp manually again.
-        timestampAdjuster.reset();
-        timestampAdjuster.setFirstSampleTimestampUs(timeUs);
+        timestampAdjuster.reset(timeUs);
       }
     }
     if (timeUs != 0 && tsBinarySearchSeeker != null) {

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaChunk.java

@@ -391,15 +391,10 @@ private void maybeLoadInitData() throws IOException {
 
   @RequiresNonNull("output")
   private void loadMedia() throws IOException {
-    if (!isMasterTimestampSource) {
-      try {
-        timestampAdjuster.waitUntilInitialized();
-      } catch (InterruptedException e) {
-        throw new InterruptedIOException();
-      }
-    } else if (timestampAdjuster.getFirstSampleTimestampUs() == TimestampAdjuster.DO_NOT_OFFSET) {
-      // We're the master and we haven't set the desired first sample timestamp yet.
-      timestampAdjuster.setFirstSampleTimestampUs(startTimeUs);
+    try {
+      timestampAdjuster.sharedInitializeOrWait(isMasterTimestampSource, startTimeUs);
+    } catch (InterruptedException e) {
+      throw new InterruptedIOException();
     }
     feedDataToExtractor(dataSource, dataSpec, mediaSegmentEncrypted);
   }

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaPeriod.java

@@ -88,6 +88,7 @@ public final class HlsMediaPeriod implements MediaPeriod, HlsSampleStreamWrapper
   private HlsSampleStreamWrapper[] enabledSampleStreamWrappers;
   // Maps sample stream wrappers to variant/rendition index by matching array positions.
   private int[][] manifestUrlIndicesPerWrapper;
+  private int audioVideoSampleStreamWrapperCount;
   private SequenceableLoader compositeSequenceableLoader;
 
   /**
@@ -315,8 +316,9 @@ public long selectTracks(
       if (wrapperEnabled) {
         newEnabledSampleStreamWrappers[newEnabledSampleStreamWrapperCount] = sampleStreamWrapper;
         if (newEnabledSampleStreamWrapperCount++ == 0) {
-          // The first enabled wrapper is responsible for initializing timestamp adjusters. This
-          // way, if enabled, variants are responsible. Else audio renditions. Else text renditions.
+          // The first enabled wrapper is always allowed to initialize timestamp adjusters. Note
+          // that the first wrapper will correspond to a variant, or else an audio rendition, or
+          // else a text rendition, in that order.
           sampleStreamWrapper.setIsTimestampMaster(true);
           if (wasReset || enabledSampleStreamWrappers.length == 0
               || sampleStreamWrapper != enabledSampleStreamWrappers[0]) {
@@ -326,7 +328,11 @@ public long selectTracks(
             forceReset = true;
           }
         } else {
-          sampleStreamWrapper.setIsTimestampMaster(false);
+          // Additional wrappers are also allowed to initialize timestamp adjusters if they contain
+          // audio or video, since they are expected to contain dense samples. Text wrappers are not
+          // permitted except in the case above in which no variant or audio rendition wrappers are
+          // enabled.
+          sampleStreamWrapper.setIsTimestampMaster(i < audioVideoSampleStreamWrapperCount);
         }
       }
     }
@@ -496,6 +502,8 @@ private void buildAndPrepareSampleStreamWrappers(long positionUs) {
         manifestUrlIndicesPerWrapper,
         overridingDrmInitData);
 
+    audioVideoSampleStreamWrapperCount = sampleStreamWrappers.size();
+
     // Subtitle stream wrappers. We can always use master playlist information to prepare these.
     for (int i = 0; i < subtitleRenditions.size(); i++) {
       Rendition subtitleRendition = subtitleRenditions.get(i);