Split TrackSelection.evalauteQueueSize in discard and cancelation.

The option to cancel ongoing loads as part of the queue size evalation
was added recently. This split out the decision to a new method so that
a TrackSelection implementation can independently cancel loads and
discard upstream data. It also clarifies that evaluateQueueSize will
only be called if there is no ongoing load.

Issue: #2848
PiperOrigin-RevId: 315659735

RELEASENOTES.md

@@ -88,6 +88,9 @@
         ([#7332](https://github.com/google/ExoPlayer/issues/7332)).
     *   Add `HttpDataSource.InvalidResponseCodeException#responseBody` field
         ([#6853](https://github.com/google/ExoPlayer/issues/6853)).
+    *   Add `TrackSelection.shouldCancelMediaChunkLoad` to check whether an
+        ongoing load should be canceled. Only supported by HLS streams so far.
+        ([#2848](https://github.com/google/ExoPlayer/issues/2848)).
 *   Video: Pass frame rate hint to `Surface.setFrameRate` on Android R devices.
 *   Text:
     *   Parse `<ruby>` and `<rt>` tags in WebVTT subtitles (rendering is coming

library/core/src/main/java/com/google/android/exoplayer2/source/MediaPeriod.java

@@ -239,8 +239,8 @@ public interface MediaPeriod extends SequenceableLoader {
    *
    * <p>This method is only called after the period has been prepared.
    *
-   * <p>A period may choose to discard buffered media so that it can be re-buffered in a different
-   * quality.
+   * <p>A period may choose to discard buffered media or cancel ongoing loads so that media can be
+   * re-buffered in a different quality.
    *
    * @param positionUs The current playback position in microseconds. If playback of this period has
    *     not yet started, the value will be the starting position in this period minus the duration

library/core/src/main/java/com/google/android/exoplayer2/source/SequenceableLoader.java

@@ -66,8 +66,8 @@ public interface SequenceableLoader {
   /**
    * Re-evaluates the buffer given the playback position.
    *
-   * <p>Re-evaluation may discard buffered media so that it can be re-buffered in a different
-   * quality.
+   * <p>Re-evaluation may discard buffered media or cancel ongoing loads so that media can be
+   * re-buffered in a different quality.
    *
    * @param positionUs The current playback position in microseconds. If playback of this period has
    *     not yet started, the value will be the starting position in this period minus the duration

library/core/src/main/java/com/google/android/exoplayer2/source/chunk/ChunkSource.java

@@ -38,8 +38,6 @@ public interface ChunkSource {
   /**
    * If the source is currently having difficulty providing chunks, then this method throws the
    * underlying error. Otherwise does nothing.
-   * <p>
-   * This method should only be called after the source has been prepared.
    *
    * @throws IOException The underlying error.
    */
@@ -47,10 +45,12 @@ public interface ChunkSource {
 
   /**
    * Evaluates whether {@link MediaChunk}s should be removed from the back of the queue.
-   * <p>
-   * Removing {@link MediaChunk}s from the back of the queue can be useful if they could be replaced
-   * with chunks of a significantly higher quality (e.g. because the available bandwidth has
-   * substantially increased).
+   *
+   * <p>Removing {@link MediaChunk}s from the back of the queue can be useful if they could be
+   * replaced with chunks of a significantly higher quality (e.g. because the available bandwidth
+   * has substantially increased).
+   *
+   * <p>Will only be called if no {@link MediaChunk} in the queue is currently loading.
    *
    * @param playbackPositionUs The current playback position.
    * @param queue The queue of buffered {@link MediaChunk}s.
@@ -85,8 +85,6 @@ public interface ChunkSource {
    * Called when the {@link ChunkSampleStream} has finished loading a chunk obtained from this
    * source.
    *
-   * <p>This method should only be called when the source is enabled.
-   *
    * @param chunk The chunk whose load has been completed.
    */
   void onChunkLoadCompleted(Chunk chunk);
@@ -95,8 +93,6 @@ public interface ChunkSource {
    * Called when the {@link ChunkSampleStream} encounters an error loading a chunk obtained from
    * this source.
    *
-   * <p>This method should only be called when the source is enabled.
-   *
    * @param chunk The chunk whose load encountered the error.
    * @param cancelable Whether the load can be canceled.
    * @param e The error.

library/core/src/main/java/com/google/android/exoplayer2/trackselection/TrackSelection.java

@@ -19,6 +19,7 @@ import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.source.TrackGroup;
+import com.google.android.exoplayer2.source.chunk.Chunk;
 import com.google.android.exoplayer2.source.chunk.MediaChunk;
 import com.google.android.exoplayer2.source.chunk.MediaChunkIterator;
 import com.google.android.exoplayer2.upstream.BandwidthMeter;
@@ -93,8 +94,8 @@ public interface TrackSelection {
 
   /**
    * Enables the track selection. Dynamic changes via {@link #updateSelectedTrack(long, long, long,
-   * List, MediaChunkIterator[])} or {@link #evaluateQueueSize(long, List)} will only happen after
-   * this call.
+   * List, MediaChunkIterator[])}, {@link #evaluateQueueSize(long, List)} or {@link
+   * #shouldCancelChunkLoad(long, Chunk, List)} will only happen after this call.
    *
    * <p>This method may not be called when the track selection is already enabled.
    */
@@ -102,8 +103,8 @@ public interface TrackSelection {
 
   /**
    * Disables this track selection. No further dynamic changes via {@link #updateSelectedTrack(long,
-   * long, long, List, MediaChunkIterator[])} or {@link #evaluateQueueSize(long, List)} will happen
-   * after this call.
+   * long, long, List, MediaChunkIterator[])}, {@link #evaluateQueueSize(long, List)} or {@link
+   * #shouldCancelChunkLoad(long, Chunk, List)} will happen after this call.
    *
    * <p>This method may only be called when the track selection is already enabled.
    */
@@ -202,7 +203,7 @@ public interface TrackSelection {
   /**
    * Updates the selected track for sources that load media in discrete {@link MediaChunk}s.
    *
-   * <p>This method may only be called when the selection is enabled.
+   * <p>This method will only be called when the selection is enabled.
    *
    * @param playbackPositionUs The current playback position in microseconds. If playback of the
    *     period to which this track selection belongs has not yet started, the value will be the
@@ -231,34 +232,77 @@ public interface TrackSelection {
       MediaChunkIterator[] mediaChunkIterators);
 
   /**
-   * May be called periodically by sources that load media in discrete {@link MediaChunk}s and
-   * support discarding of buffered chunks in order to re-buffer using a different selected track.
    * Returns the number of chunks that should be retained in the queue.
-   * <p>
-   * To avoid excessive re-buffering, implementations should normally return the size of the queue.
-   * An example of a case where a smaller value may be returned is if network conditions have
+   *
+   * <p>May be called by sources that load media in discrete {@link MediaChunk MediaChunks} and
+   * support discarding of buffered chunks.
+   *
+   * <p>To avoid excessive re-buffering, implementations should normally return the size of the
+   * queue. An example of a case where a smaller value may be returned is if network conditions have
    * improved dramatically, allowing chunks to be discarded and re-buffered in a track of
    * significantly higher quality. Discarding chunks may allow faster switching to a higher quality
-   * track in this case. This method may only be called when the selection is enabled.
+   * track in this case.
+   *
+   * <p>Note that even if the source supports discarding of buffered chunks, the actual number of
+   * discarded chunks is not guaranteed. The source will call {@link #updateSelectedTrack(long,
+   * long, long, List, MediaChunkIterator[])} with the updated queue of chunks before loading a new
+   * chunk to allow switching to another quality.
+   *
+   * <p>This method will only be called when the selection is enabled and none of the {@link
+   * MediaChunk MediaChunks} in the queue are currently loading.
    *
    * @param playbackPositionUs The current playback position in microseconds. If playback of the
    *     period to which this track selection belongs has not yet started, the value will be the
    *     starting position in the period minus the duration of any media in previous periods still
    *     to be played.
-   * @param queue The queue of buffered {@link MediaChunk}s. Must not be modified.
+   * @param queue The queue of buffered {@link MediaChunk MediaChunks}. Must not be modified.
    * @return The number of chunks to retain in the queue.
    */
   int evaluateQueueSize(long playbackPositionUs, List<? extends MediaChunk> queue);
 
   /**
+   * Returns whether an ongoing load of a chunk should be canceled.
+   *
+   * <p>May be called by sources that load media in discrete {@link MediaChunk MediaChunks} and
+   * support canceling the ongoing chunk load. The ongoing chunk load is either the last {@link
+   * MediaChunk} in the queue or another type of {@link Chunk}, for example, if the source loads
+   * initialization or encryption data.
+   *
+   * <p>To avoid excessive re-buffering, implementations should normally return {@code false}. An
+   * example where {@code true} might be returned is if a load of a high quality chunk gets stuck
+   * and canceling this load in favor of a lower quality alternative may avoid a rebuffer.
+   *
+   * <p>The source will call {@link #evaluateQueueSize(long, List)} after the cancelation finishes
+   * to allow discarding of chunks, and {@link #updateSelectedTrack(long, long, long, List,
+   * MediaChunkIterator[])} before loading a new chunk to allow switching to another quality.
+   *
+   * <p>This method will only be called when the selection is enabled.
+   *
+   * @param playbackPositionUs The current playback position in microseconds. If playback of the
+   *     period to which this track selection belongs has not yet started, the value will be the
+   *     starting position in the period minus the duration of any media in previous periods still
+   *     to be played.
+   * @param loadingChunk The currently loading {@link Chunk} that will be canceled if this method
+   *     returns {@code true}.
+   * @param queue The queue of buffered {@link MediaChunk MediaChunks}, including the {@code
+   *     loadingChunk} if it's a {@link MediaChunk}. Must not be modified.
+   * @return Whether the ongoing load of {@code loadingChunk} should be canceled.
+   */
+  default boolean shouldCancelChunkLoad(
+      long playbackPositionUs, Chunk loadingChunk, List<? extends MediaChunk> queue) {
+    return false;
+  }
+
+  /**
    * Attempts to blacklist the track at the specified index in the selection, making it ineligible
    * for selection by calls to {@link #updateSelectedTrack(long, long, long, List,
-   * MediaChunkIterator[])} for the specified period of time. Blacklisting will fail if all other
-   * tracks are currently blacklisted. If blacklisting the currently selected track, note that it
-   * will remain selected until the next call to {@link #updateSelectedTrack(long, long, long, List,
-   * MediaChunkIterator[])}.
+   * MediaChunkIterator[])} for the specified period of time.
+   *
+   * <p>Blacklisting will fail if all other tracks are currently blacklisted. If blacklisting the
+   * currently selected track, note that it will remain selected until the next call to {@link
+   * #updateSelectedTrack(long, long, long, List, MediaChunkIterator[])}.
    *
-   * <p>This method may only be called when the selection is enabled.
+   * <p>This method will only be called when the selection is enabled.
    *
    * @param index The index of the track in the selection.
    * @param blacklistDurationMs The duration of time for which the track should be blacklisted, in

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

@@ -458,6 +458,8 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
    * could be replaced with chunks of a significantly higher quality (e.g. because the available
    * bandwidth has substantially increased).
    *
+   * <p>Will only be called if no {@link MediaChunk} in the queue is currently loading.
+   *
    * @param playbackPositionUs The current playback position, in microseconds.
    * @param queue The queue of buffered {@link MediaChunk MediaChunks}.
    * @return The preferred queue size.
@@ -469,6 +471,22 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     return trackSelection.evaluateQueueSize(playbackPositionUs, queue);
   }
 
+  /**
+   * Returns whether an ongoing load of a chunk should be canceled.
+   *
+   * @param playbackPositionUs The current playback position, in microseconds.
+   * @param loadingChunk The currently loading {@link Chunk}.
+   * @param queue The queue of buffered {@link MediaChunk MediaChunks}.
+   * @return Whether the ongoing load of {@code loadingChunk} should be canceled.
+   */
+  public boolean shouldCancelLoad(
+      long playbackPositionUs, Chunk loadingChunk, List<? extends MediaChunk> queue) {
+    if (fatalError != null) {
+      return false;
+    }
+    return trackSelection.shouldCancelChunkLoad(playbackPositionUs, loadingChunk, queue);
+  }
+
   // Private methods.
 
   /**

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

@@ -133,6 +133,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   private final ArrayList<HlsSampleStream> hlsSampleStreams;
   private final Map<String, DrmInitData> overridingDrmInitData;
 
+  @Nullable private Chunk loadingChunk;
   private HlsSampleQueue[] sampleQueues;
   private int[] sampleQueueTrackIds;
   private Set<Integer> sampleQueueMappingDoneByType;
@@ -674,6 +675,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     if (isMediaChunk(loadable)) {
       initMediaChunkLoad((HlsMediaChunk) loadable);
     }
+    loadingChunk = loadable;
     long elapsedRealtimeMs =
         loader.startLoading(
             loadable, this, loadErrorHandlingPolicy.getMinimumLoadableRetryCount(loadable.type));
@@ -700,14 +702,16 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
       return;
     }
 
-    int currentQueueSize = mediaChunks.size();
-    int preferredQueueSize = chunkSource.getPreferredQueueSize(positionUs, readOnlyMediaChunks);
-    if (currentQueueSize <= preferredQueueSize) {
+    if (loader.isLoading()) {
+      Assertions.checkNotNull(loadingChunk);
+      if (chunkSource.shouldCancelLoad(positionUs, loadingChunk, readOnlyMediaChunks)) {
+        loader.cancelLoading();
+      }
       return;
     }
-    if (loader.isLoading()) {
-      loader.cancelLoading();
-    } else {
+
+    int preferredQueueSize = chunkSource.getPreferredQueueSize(positionUs, readOnlyMediaChunks);
+    if (preferredQueueSize < mediaChunks.size()) {
       discardUpstream(preferredQueueSize);
     }
   }
@@ -716,6 +720,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
   @Override
   public void onLoadCompleted(Chunk loadable, long elapsedRealtimeMs, long loadDurationMs) {
+    loadingChunk = null;
     chunkSource.onChunkLoadCompleted(loadable);
     LoadEventInfo loadEventInfo =
         new LoadEventInfo(
@@ -746,6 +751,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   @Override
   public void onLoadCanceled(
       Chunk loadable, long elapsedRealtimeMs, long loadDurationMs, boolean released) {
+    loadingChunk = null;
     LoadEventInfo loadEventInfo =
         new LoadEventInfo(
             loadable.loadTaskId,
@@ -841,6 +847,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
         error,
         wasCanceled);
     if (wasCanceled) {
+      loadingChunk = null;
       loadErrorHandlingPolicy.onLoadTaskConcluded(loadable.loadTaskId);
     }
 
@@ -885,7 +892,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
     if (newQueueSize == C.LENGTH_UNSET) {
       return;
     }
-    
+
     long endTimeUs = getLastMediaChunk().endTimeUs;
     HlsMediaChunk firstRemovedChunk = discardUpstreamMediaChunksFromIndex(newQueueSize);
     if (mediaChunks.isEmpty()) {