Add FilterableMediaPeriod interface and SmoothStreaming implementation.

This interface allows to put the mapping from tracks to StreamKeys in the same place
where we map manifest to tracks.

PiperOrigin-RevId: 225377033

library/core/src/main/java/com/google/android/exoplayer2/offline/StreamKey.java

@@ -19,11 +19,11 @@ import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 
 /**
- * Identifies a stream in a {@link FilterableManifest} by the index of the containing period, the
- * index of the containing group within the period, and the index of the track within the group.
+ * A key for a subset of media which can be separately loaded (a "stream").
  *
- * <p>Note that the interpretation of period, group and index depends on the type of manifest being
- * filtered.
+ * <p>The stream key consists of a period index, a group index within the period and a track index
+ * within the group. The interpretation of these indices depends on the type of media for which the
+ * stream key is used.
  */
 public final class StreamKey implements Comparable<StreamKey> {
 

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

@@ -19,8 +19,11 @@ import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlayer;
 import com.google.android.exoplayer2.SeekParameters;
 import com.google.android.exoplayer2.Timeline;
+import com.google.android.exoplayer2.offline.StreamKey;
 import com.google.android.exoplayer2.trackselection.TrackSelection;
 import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
 import org.checkerframework.checker.nullness.compatqual.NullableType;
 
 /**
@@ -84,6 +87,22 @@ public interface MediaPeriod extends SequenceableLoader {
   TrackGroupArray getTrackGroups();
 
   /**
+   * Returns a list of {@link StreamKey stream keys} which allow to filter the media in this period
+   * to load only the parts needed to play the provided {@link TrackSelection}.
+   *
+   * <p>This method is only called after the period has been prepared.
+   *
+   * @param trackSelection The {@link TrackSelection} describing the tracks for which stream keys
+   *     are requested.
+   * @return The corresponding {@link StreamKey stream keys} for the selected tracks, or an empty
+   *     list if filtering is not possible and the entire media needs to be loaded to play the
+   *     selected tracks.
+   */
+  default List<StreamKey> getStreamKeys(TrackSelection trackSelection) {
+    return Collections.emptyList();
+  }
+
+  /**
    * Performs a track selection.
    *
    * <p>The call receives track {@code selections} for each renderer, {@code mayRetainStreamFlags}

library/smoothstreaming/src/main/java/com/google/android/exoplayer2/source/smoothstreaming/SsMediaPeriod.java

@@ -20,6 +20,7 @@ import android.util.Base64;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.SeekParameters;
 import com.google.android.exoplayer2.extractor.mp4.TrackEncryptionBox;
+import com.google.android.exoplayer2.offline.StreamKey;
 import com.google.android.exoplayer2.source.CompositeSequenceableLoaderFactory;
 import com.google.android.exoplayer2.source.MediaPeriod;
 import com.google.android.exoplayer2.source.MediaSourceEventListener.EventDispatcher;
@@ -37,12 +38,11 @@ import com.google.android.exoplayer2.upstream.LoaderErrorThrower;
 import com.google.android.exoplayer2.upstream.TransferListener;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.List;
 
-/**
- * A SmoothStreaming {@link MediaPeriod}.
- */
-/* package */ final class SsMediaPeriod implements MediaPeriod,
-    SequenceableLoader.Callback<ChunkSampleStream<SsChunkSource>> {
+/** A SmoothStreaming {@link MediaPeriod}. */
+/* package */ final class SsMediaPeriod
+    implements MediaPeriod, SequenceableLoader.Callback<ChunkSampleStream<SsChunkSource>> {
 
   private static final int INITIALIZATION_VECTOR_SIZE = 8;
 
@@ -112,6 +112,8 @@ import java.util.ArrayList;
     eventDispatcher.mediaPeriodReleased();
   }
 
+  // MediaPeriod implementation.
+
   @Override
   public void prepare(Callback callback, long positionUs) {
     this.callback = callback;
@@ -158,6 +160,16 @@ import java.util.ArrayList;
   }
 
   @Override
+  public List<StreamKey> getStreamKeys(TrackSelection trackSelection) {
+    List<StreamKey> streamKeys = new ArrayList<>(trackSelection.length());
+    int streamElementIndex = trackGroups.indexOf(trackSelection.getTrackGroup());
+    for (int i = 0; i < trackSelection.length(); i++) {
+      streamKeys.add(new StreamKey(streamElementIndex, trackSelection.getIndexInTrackGroup(i)));
+    }
+    return streamKeys;
+  }
+
+  @Override
   public void discardBuffer(long positionUs, boolean toKeyframe) {
     for (ChunkSampleStream<SsChunkSource> sampleStream : sampleStreams) {
       sampleStream.discardBuffer(positionUs, toKeyframe);
@@ -211,7 +223,7 @@ import java.util.ArrayList;
     return positionUs;
   }
 
-  // SequenceableLoader.Callback implementation
+  // SequenceableLoader.Callback implementation.
 
   @Override
   public void onContinueLoadingRequested(ChunkSampleStream<SsChunkSource> sampleStream) {
@@ -277,5 +289,4 @@ import java.util.ArrayList;
     data[firstPosition] = data[secondPosition];
     data[secondPosition] = temp;
   }
-
 }