Allow more flexible loading strategy when loading multiple sub streams.

Currently for a DASH ChunkSource that consists of multiple sub-streams, we
always use a CompositeSequenceableLoader, which only allows the furthest behind
loader or any loader that are behind current playback position to continue
loading.
This changes allow clients to have more flexibility when deciding the loading
strategy:
- They can construct a different kind of composite SequenceableLoader from
the sub-loaders, and use it by injecting a different CompositeSequeableLoaderFactory accordingly.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=176363870

RELEASENOTES.md

@@ -2,8 +2,12 @@
 
 ### dev-v2 (not yet released) ###
 
-* Add Builder to ExtractorMediaSource, HlsMediaSource, SsMediaSource,
-  DashMediaSource, SingleSampleMediaSource.
+* Allow more flexible loading strategy when playing media containing multiple
+  sub-streams, by allowing injection of custom `CompositeSequenceableLoader`
+  factories through `DashMediaSource.Builder`, `HlsMediaSource.Builder`,
+  `SsMediaSource.Builder`, and `MergingMediaSource`.
+* Add Builder to `ExtractorMediaSource`, `HlsMediaSource`, `SsMediaSource`,
+  `DashMediaSource`, `SingleSampleMediaSource`.
 * DASH:
   * Support in-MPD EventStream.
 * Allow a back-buffer of media to be retained behind the current playback

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

@@ -20,9 +20,9 @@
 /**
  * A {@link SequenceableLoader} that encapsulates multiple other {@link SequenceableLoader}s.
  */
-public final class CompositeSequenceableLoader implements SequenceableLoader {
+public class CompositeSequenceableLoader implements SequenceableLoader {
 
-  private final SequenceableLoader[] loaders;
+  protected final SequenceableLoader[] loaders;
 
   public CompositeSequenceableLoader(SequenceableLoader[] loaders) {
     this.loaders = loaders;
@@ -53,7 +53,7 @@ public final long getNextLoadPositionUs() {
   }
 
   @Override
-  public final boolean continueLoading(long positionUs) {
+  public boolean continueLoading(long positionUs) {
     boolean madeProgress = false;
     boolean madeProgressThisIteration;
     do {

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

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer2.source;
+
+/**
+ * A factory to create composite {@link SequenceableLoader}s.
+ */
+public interface CompositeSequenceableLoaderFactory {
+
+  /**
+   * Creates a composite {@link SequenceableLoader}.
+   *
+   * @param loaders The sub-loaders that make up the {@link SequenceableLoader} to be built.
+   * @return A composite {@link SequenceableLoader} that comprises the given loaders.
+   */
+  SequenceableLoader createCompositeSequenceableLoader(SequenceableLoader... loaders);
+
+}

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

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer2.source;
+
+/**
+ * Default implementation of {@link CompositeSequenceableLoaderFactory}.
+ */
+public final class DefaultCompositeSequenceableLoaderFactory
+    implements CompositeSequenceableLoaderFactory {
+
+  @Override
+  public SequenceableLoader createCompositeSequenceableLoader(SequenceableLoader... loaders) {
+    return new CompositeSequenceableLoader(loaders);
+  }
+
+}

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

@@ -30,15 +30,18 @@
   public final MediaPeriod[] periods;
 
   private final IdentityHashMap<SampleStream, Integer> streamPeriodIndices;
+  private final CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory;
 
   private Callback callback;
   private int pendingChildPrepareCount;
   private TrackGroupArray trackGroups;
 
   private MediaPeriod[] enabledPeriods;
-  private SequenceableLoader sequenceableLoader;
+  private SequenceableLoader compositeSequenceableLoader;
 
-  public MergingMediaPeriod(MediaPeriod... periods) {
+  public MergingMediaPeriod(CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory,
+      MediaPeriod... periods) {
+    this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
     this.periods = periods;
     streamPeriodIndices = new IdentityHashMap<>();
   }
@@ -124,7 +127,8 @@ public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamF
     // Update the local state.
     enabledPeriods = new MediaPeriod[enabledPeriodsList.size()];
     enabledPeriodsList.toArray(enabledPeriods);
-    sequenceableLoader = new CompositeSequenceableLoader(enabledPeriods);
+    compositeSequenceableLoader =
+        compositeSequenceableLoaderFactory.createCompositeSequenceableLoader(enabledPeriods);
     return positionUs;
   }
 
@@ -137,12 +141,12 @@ public void discardBuffer(long positionUs, boolean toKeyframe) {
 
   @Override
   public boolean continueLoading(long positionUs) {
-    return sequenceableLoader.continueLoading(positionUs);
+    return compositeSequenceableLoader.continueLoading(positionUs);
   }
 
   @Override
   public long getNextLoadPositionUs() {
-    return sequenceableLoader.getNextLoadPositionUs();
+    return compositeSequenceableLoader.getNextLoadPositionUs();
   }
 
   @Override
@@ -168,7 +172,7 @@ public long readDiscontinuity() {
 
   @Override
   public long getBufferedPositionUs() {
-    return sequenceableLoader.getBufferedPositionUs();
+    return compositeSequenceableLoader.getBufferedPositionUs();
   }
 
   @Override

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

@@ -74,6 +74,7 @@ public IllegalMergeException(@Reason int reason) {
   private final MediaSource[] mediaSources;
   private final ArrayList<MediaSource> pendingTimelineSources;
   private final Timeline.Window window;
+  private final CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory;
 
   private Listener listener;
   private Timeline primaryTimeline;
@@ -85,7 +86,19 @@ public IllegalMergeException(@Reason int reason) {
    * @param mediaSources The {@link MediaSource}s to merge.
    */
   public MergingMediaSource(MediaSource... mediaSources) {
+    this(new DefaultCompositeSequenceableLoaderFactory(), mediaSources);
+  }
+
+  /**
+   * @param compositeSequenceableLoaderFactory A factory to create composite
+   *     {@link SequenceableLoader}s for when this media source loads data from multiple streams
+   *     (video, audio etc...).
+   * @param mediaSources The {@link MediaSource}s to merge.
+   */
+  public MergingMediaSource(CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory,
+      MediaSource... mediaSources) {
     this.mediaSources = mediaSources;
+    this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
     pendingTimelineSources = new ArrayList<>(Arrays.asList(mediaSources));
     window = new Timeline.Window();
     periodCount = PERIOD_COUNT_UNSET;
@@ -121,7 +134,7 @@ public MediaPeriod createPeriod(MediaPeriodId id, Allocator allocator) {
     for (int i = 0; i < periods.length; i++) {
       periods[i] = mediaSources[i].createPeriod(id, allocator);
     }
-    return new MergingMediaPeriod(periods);
+    return new MergingMediaPeriod(compositeSequenceableLoaderFactory, periods);
   }
 
   @Override

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaPeriod.java

@@ -21,7 +21,7 @@
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.source.AdaptiveMediaSourceEventListener.EventDispatcher;
-import com.google.android.exoplayer2.source.CompositeSequenceableLoader;
+import com.google.android.exoplayer2.source.CompositeSequenceableLoaderFactory;
 import com.google.android.exoplayer2.source.EmptySampleStream;
 import com.google.android.exoplayer2.source.MediaPeriod;
 import com.google.android.exoplayer2.source.SampleStream;
@@ -64,19 +64,21 @@
   private final Allocator allocator;
   private final TrackGroupArray trackGroups;
   private final TrackGroupInfo[] trackGroupInfos;
+  private final CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory;
 
   private Callback callback;
   private ChunkSampleStream<DashChunkSource>[] sampleStreams;
   private EventSampleStream[] eventSampleStreams;
-  private CompositeSequenceableLoader sequenceableLoader;
+  private SequenceableLoader compositeSequenceableLoader;
   private DashManifest manifest;
   private int periodIndex;
   private List<EventStream> eventStreams;
 
   public DashMediaPeriod(int id, DashManifest manifest, int periodIndex,
-      DashChunkSource.Factory chunkSourceFactory,  int minLoadableRetryCount,
+      DashChunkSource.Factory chunkSourceFactory, int minLoadableRetryCount,
       EventDispatcher eventDispatcher, long elapsedRealtimeOffset,
-      LoaderErrorThrower manifestLoaderErrorThrower, Allocator allocator) {
+      LoaderErrorThrower manifestLoaderErrorThrower, Allocator allocator,
+      CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory) {
     this.id = id;
     this.manifest = manifest;
     this.periodIndex = periodIndex;
@@ -86,9 +88,11 @@ public DashMediaPeriod(int id, DashManifest manifest, int periodIndex,
     this.elapsedRealtimeOffset = elapsedRealtimeOffset;
     this.manifestLoaderErrorThrower = manifestLoaderErrorThrower;
     this.allocator = allocator;
+    this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
     sampleStreams = newSampleStreamArray(0);
     eventSampleStreams = new EventSampleStream[0];
-    sequenceableLoader = new CompositeSequenceableLoader(sampleStreams);
+    compositeSequenceableLoader =
+        compositeSequenceableLoaderFactory.createCompositeSequenceableLoader(sampleStreams);
     Period period = manifest.getPeriod(periodIndex);
     eventStreams = period.eventStreams;
     Pair<TrackGroupArray, TrackGroupInfo[]> result = buildTrackGroups(period.adaptationSets,
@@ -163,7 +167,8 @@ public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamF
     primarySampleStreams.values().toArray(sampleStreams);
     eventSampleStreams = new EventSampleStream[eventSampleStreamList.size()];
     eventSampleStreamList.toArray(eventSampleStreams);
-    sequenceableLoader = new CompositeSequenceableLoader(sampleStreams);
+    compositeSequenceableLoader =
+        compositeSequenceableLoaderFactory.createCompositeSequenceableLoader(sampleStreams);
     return positionUs;
   }
 
@@ -267,12 +272,12 @@ public void discardBuffer(long positionUs, boolean toKeyframe) {
 
   @Override
   public boolean continueLoading(long positionUs) {
-    return sequenceableLoader.continueLoading(positionUs);
+    return compositeSequenceableLoader.continueLoading(positionUs);
   }
 
   @Override
   public long getNextLoadPositionUs() {
-    return sequenceableLoader.getNextLoadPositionUs();
+    return compositeSequenceableLoader.getNextLoadPositionUs();
   }
 
   @Override
@@ -282,7 +287,7 @@ public long readDiscontinuity() {
 
   @Override
   public long getBufferedPositionUs() {
-    return sequenceableLoader.getBufferedPositionUs();
+    return compositeSequenceableLoader.getBufferedPositionUs();
   }
 
   @Override

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaSource.java

@@ -28,8 +28,11 @@
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.source.AdaptiveMediaSourceEventListener;
 import com.google.android.exoplayer2.source.AdaptiveMediaSourceEventListener.EventDispatcher;
+import com.google.android.exoplayer2.source.CompositeSequenceableLoaderFactory;
+import com.google.android.exoplayer2.source.DefaultCompositeSequenceableLoaderFactory;
 import com.google.android.exoplayer2.source.MediaPeriod;
 import com.google.android.exoplayer2.source.MediaSource;
+import com.google.android.exoplayer2.source.SequenceableLoader;
 import com.google.android.exoplayer2.source.dash.manifest.DashManifest;
 import com.google.android.exoplayer2.source.dash.manifest.DashManifestParser;
 import com.google.android.exoplayer2.source.dash.manifest.UtcTimingElement;
@@ -71,6 +74,7 @@ public static final class Builder {
     private ParsingLoadable.Parser<? extends DashManifest> manifestParser;
     private AdaptiveMediaSourceEventListener eventListener;
     private Handler eventHandler;
+    private CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory;
 
     private int minLoadableRetryCount;
     private long livePresentationDelayMs;
@@ -171,6 +175,22 @@ public Builder setManifestParser(
       return this;
     }
 
+    /**
+     * Sets the factory to create composite {@link SequenceableLoader}s for when this media source
+     * loads data from multiple streams (video, audio etc...). The default is an instance of
+     * {@link DefaultCompositeSequenceableLoaderFactory}.
+     *
+     * @param compositeSequenceableLoaderFactory A factory to create composite
+     *     {@link SequenceableLoader}s for when this media source loads data from multiple streams
+     *     (video, audio etc...).
+     * @return This builder.
+     */
+    public Builder setCompositeSequenceableLoaderFactory(
+        CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory) {
+      this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
+      return this;
+    }
+
     /**
      * Builds a new {@link DashMediaSource} using the current parameters.
      * <p>
@@ -186,9 +206,12 @@ public DashMediaSource build() {
       if (loadableManifestUri && manifestParser == null) {
         manifestParser = new DashManifestParser();
       }
+      if (compositeSequenceableLoaderFactory == null) {
+        compositeSequenceableLoaderFactory = new DefaultCompositeSequenceableLoaderFactory();
+      }
       return new DashMediaSource(manifest, manifestUri, manifestDataSourceFactory, manifestParser,
-          chunkSourceFactory, minLoadableRetryCount, livePresentationDelayMs, eventHandler,
-          eventListener);
+          chunkSourceFactory, compositeSequenceableLoaderFactory, minLoadableRetryCount,
+          livePresentationDelayMs, eventHandler, eventListener);
     }
 
   }
@@ -226,6 +249,7 @@ public DashMediaSource build() {
   private final boolean sideloadedManifest;
   private final DataSource.Factory manifestDataSourceFactory;
   private final DashChunkSource.Factory chunkSourceFactory;
+  private final CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory;
   private final int minLoadableRetryCount;
   private final long livePresentationDelayMs;
   private final EventDispatcher eventDispatcher;
@@ -280,7 +304,8 @@ public DashMediaSource(DashManifest manifest, DashChunkSource.Factory chunkSourc
   public DashMediaSource(DashManifest manifest, DashChunkSource.Factory chunkSourceFactory,
       int minLoadableRetryCount, Handler eventHandler, AdaptiveMediaSourceEventListener
       eventListener) {
-    this(manifest, null, null, null, chunkSourceFactory, minLoadableRetryCount,
+    this(manifest, null, null, null, chunkSourceFactory,
+        new DefaultCompositeSequenceableLoaderFactory(), minLoadableRetryCount,
         DEFAULT_LIVE_PRESENTATION_DELAY_PREFER_MANIFEST_MS, eventHandler, eventListener);
   }
 
@@ -356,14 +381,16 @@ public DashMediaSource(Uri manifestUri, DataSource.Factory manifestDataSourceFac
       long livePresentationDelayMs, Handler eventHandler,
       AdaptiveMediaSourceEventListener eventListener) {
     this(null, manifestUri, manifestDataSourceFactory, manifestParser, chunkSourceFactory,
-        minLoadableRetryCount, livePresentationDelayMs, eventHandler, eventListener);
+        new DefaultCompositeSequenceableLoaderFactory(), minLoadableRetryCount,
+        livePresentationDelayMs, eventHandler, eventListener);
   }
 
   private DashMediaSource(DashManifest manifest, Uri manifestUri,
       DataSource.Factory manifestDataSourceFactory,
       ParsingLoadable.Parser<? extends DashManifest> manifestParser,
-      DashChunkSource.Factory chunkSourceFactory, int minLoadableRetryCount,
-      long livePresentationDelayMs, Handler eventHandler,
+      DashChunkSource.Factory chunkSourceFactory,
+      CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory,
+      int minLoadableRetryCount, long livePresentationDelayMs, Handler eventHandler,
       AdaptiveMediaSourceEventListener eventListener) {
     this.manifest = manifest;
     this.manifestUri = manifestUri;
@@ -372,6 +399,7 @@ private DashMediaSource(DashManifest manifest, Uri manifestUri,
     this.chunkSourceFactory = chunkSourceFactory;
     this.minLoadableRetryCount = minLoadableRetryCount;
     this.livePresentationDelayMs = livePresentationDelayMs;
+    this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
     sideloadedManifest = manifest != null;
     eventDispatcher = new EventDispatcher(eventHandler, eventListener);
     manifestUriLock = new Object();
@@ -438,7 +466,7 @@ public MediaPeriod createPeriod(MediaPeriodId periodId, Allocator allocator) {
         manifest.getPeriod(periodIndex).startMs);
     DashMediaPeriod mediaPeriod = new DashMediaPeriod(firstPeriodId + periodIndex, manifest,
         periodIndex, chunkSourceFactory, minLoadableRetryCount, periodEventDispatcher,
-        elapsedRealtimeOffsetMs, loaderErrorThrower, allocator);
+        elapsedRealtimeOffsetMs, loaderErrorThrower, allocator, compositeSequenceableLoaderFactory);
     periodsById.put(mediaPeriod.id, mediaPeriod);
     return mediaPeriod;
   }