Add support for resetting the AudioTrack stream type.

This is only exposed on the MediaCodecAudioTrackRenderer in v1.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139891484

library/src/main/java/com/google/android/exoplayer/MediaCodecAudioTrackRenderer.java

@@ -69,21 +69,33 @@ public interface EventListener extends MediaCodecTrackRenderer.EventListener {
   }
 
   /**
-   * The type of a message that can be passed to an instance of this class via
+   * A type of a message that can be passed to an instance of this class via
    * {@link ExoPlayer#sendMessage} or {@link ExoPlayer#blockingSendMessage}. The message object
    * should be a {@link Float} with 0 being silence and 1 being unity gain.
    */
   public static final int MSG_SET_VOLUME = 1;
 
   /**
-   * The type of a message that can be passed to an instance of this class via
+   * A type of a message that can be passed to an instance of this class via
    * {@link ExoPlayer#sendMessage} or {@link ExoPlayer#blockingSendMessage}. The message object
    * should be a {@link android.media.PlaybackParams}, which will be used to configure the
    * underlying {@link android.media.AudioTrack}. The message object should not be modified by the
    * caller after it has been passed
    */
   public static final int MSG_SET_PLAYBACK_PARAMS = 2;
 
+  /**
+   * A type of a message that can be passed to an instance of this class via
+   * {@link ExoPlayer#sendMessage} or {@link ExoPlayer#blockingSendMessage}. The message object
+   * should be an integer stream type accepted by {@link android.media.AudioTrack}'s constructor
+   * (see {@link android.media.AudioTrack#AudioTrack(int, int, int, int, int, int)}).
+   * <p>
+   * Note that when the stream type changes, the AudioTrack must be reinitialized, which can
+   * introduce a brief gap in audio output. Note also that tracks in the same audio session must
+   * share the same routing, so a new audio session id will be generated.
+   */
+  public static final int MSG_SET_STREAM_TYPE = 3;
+
   private final EventListener eventListener;
   private final AudioTrack audioTrack;
 
@@ -441,6 +453,12 @@ public void handleMessage(int messageType, Object message) throws ExoPlaybackExc
       case MSG_SET_PLAYBACK_PARAMS:
         audioTrack.setPlaybackParams((PlaybackParams) message);
         break;
+      case MSG_SET_STREAM_TYPE:
+        int streamType = (Integer) message;
+        if (audioTrack.setStreamType(streamType)) {
+          audioSessionId = AudioTrack.SESSION_ID_NOT_SET;
+        }
+        break;
       default:
         super.handleMessage(messageType, message);
         break;

library/src/main/java/com/google/android/exoplayer/audio/AudioTrack.java

@@ -184,7 +184,6 @@ public InvalidAudioTrackTimestampException(String message) {
   public static boolean failOnSpuriousAudioTimestamp = false;
 
   private final AudioCapabilities audioCapabilities;
-  private final int streamType;
   private final ConditionVariable releasingConditionVariable;
   private final long[] playheadOffsets;
   private final AudioTrackUtil audioTrackUtil;
@@ -197,6 +196,7 @@ public InvalidAudioTrackTimestampException(String message) {
   private android.media.AudioTrack audioTrack;
   private int sampleRate;
   private int channelConfig;
+  private int streamType;
   private int sourceEncoding;
   private int targetEncoding;
   private boolean passthrough;
@@ -243,7 +243,6 @@ public AudioTrack() {
    */
   public AudioTrack(AudioCapabilities audioCapabilities, int streamType) {
     this.audioCapabilities = audioCapabilities;
-    this.streamType = streamType;
     releasingConditionVariable = new ConditionVariable(true);
     if (Util.SDK_INT >= 18) {
       try {
@@ -261,6 +260,7 @@ public AudioTrack(AudioCapabilities audioCapabilities, int streamType) {
       audioTrackUtil = new AudioTrackUtil();
     }
     playheadOffsets = new long[MAX_PLAYHEAD_OFFSET_COUNT];
+    this.streamType = streamType;
     volume = 1.0f;
     startMediaTimeState = START_NOT_SET;
   }
@@ -702,6 +702,24 @@ public void setPlaybackParams(PlaybackParams playbackParams) {
     audioTrackUtil.setPlaybackParameters(playbackParams);
   }
 
+  /**
+   * Sets the stream type for audio track. If the stream type has changed, {@link #isInitialized()}
+   * will return {@code false} and the caller must re-{@link #initialize(int)} the audio track
+   * before writing more data. The caller must not reuse the audio session identifier when
+   * re-initializing with a new stream type.
+   *
+   * @param streamType The stream type to use for audio output.
+   * @return Whether the stream type changed.
+   */
+  public boolean setStreamType(int streamType) {
+    if (this.streamType == streamType) {
+      return false;
+    }
+    this.streamType = streamType;
+    reset();
+    return true;
+  }
+
   /**
    * Sets the playback volume.
    */