DefaultTrackSelector: Constrain audio channel count

The track selector will select multi-channel formats when those can be
spatialized, otherwise the selector will prefer stereo/mono audio
tracks. When the device supports audio spatialization (Android 12L+),
the DefaultTrackSelector will monitor for changes in the platform
Spatializer and trigger a new track selection upon a
Spatializer change event.

Devices with a `television` UI mode are excluded from audio channel
count constraints.

#minor-release

PiperOrigin-RevId: 453957269

RELEASENOTES.md

@@ -39,6 +39,24 @@
         `DefaultTrackSelector.Parameters.buildUpon` to return
         `DefaultTrackSelector.Parameters.Builder` instead of the deprecated
         `DefaultTrackSelector.ParametersBuilder`.
+    *   Add
+        `DefaultTrackSelector.Parameters.constrainAudioChannelCountToDeviceCapabilities`.
+        which is enabled by default. When enabled, the `DefaultTrackSelector`
+        will prefer audio tracks whose channel count does not exceed the device
+        output capabilities. On handheld devices, the `DefaultTrackSelector`
+        will prefer stereo/mono over multichannel audio formats, unless the
+        multichannel format can be
+        [Spatialized](https://developer.android.com/reference/android/media/Spatializer)
+        (Android 12L+) or is a Dolby surround sound format. In addition, on
+        devices that support audio spatialization, the `DefaultTrackSelector`
+        will monitor for changes in the
+        [Spatializer properties](https://developer.android.com/reference/android/media/Spatializer.OnSpatializerStateChangedListener)
+        and trigger a new track selection upon these. Devices with a
+        `television`
+        [UI mode](https://developer.android.com/guide/topics/resources/providing-resources#UiModeQualifier)
+        are excluded from these constraints and the format with the highest
+        channel count will be preferred. To enable this feature, the
+        `DefaultTrackSelector` instance must be constructed with a `Context`.
 *   Video:
     *   Rename `DummySurface` to `PlaceholderSurface`.
     *   Add AV1 support to the `MediaCodecVideoRenderer.getCodecMaxInputSize`.
@@ -171,6 +189,8 @@
         `DEFAULT_TRACK_SELECTOR_PARAMETERS` constants. Use
         `getDefaultTrackSelectorParameters(Context)` instead when possible, and
         `DEFAULT_TRACK_SELECTOR_PARAMETERS_WITHOUT_CONTEXT` otherwise.
+    *   Remove constructor `DefaultTrackSelector(ExoTrackSelection.Factory)`.
+        Use `DefaultTrackSelector(Context, ExoTrackSelection.Factory)` instead.
 
 ### 1.0.0-alpha03 (2022-03-14)
 

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/ExoPlayerImpl.java

@@ -380,6 +380,7 @@ import java.util.concurrent.TimeoutException;
       deviceInfo = createDeviceInfo(streamVolumeManager);
       videoSize = VideoSize.UNKNOWN;
 
+      trackSelector.setAudioAttributes(audioAttributes);
       sendRendererMessage(TRACK_TYPE_AUDIO, MSG_SET_AUDIO_SESSION_ID, audioSessionId);
       sendRendererMessage(TRACK_TYPE_VIDEO, MSG_SET_AUDIO_SESSION_ID, audioSessionId);
       sendRendererMessage(TRACK_TYPE_AUDIO, MSG_SET_AUDIO_ATTRIBUTES, audioAttributes);
@@ -1375,6 +1376,7 @@ import java.util.concurrent.TimeoutException;
     }
 
     audioFocusManager.setAudioAttributes(handleAudioFocus ? newAudioAttributes : null);
+    trackSelector.setAudioAttributes(newAudioAttributes);
     boolean playWhenReady = getPlayWhenReady();
     @AudioFocusManager.PlayerCommand
     int playerCommand = audioFocusManager.updateAudioFocus(playWhenReady, getPlaybackState());

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/offline/DownloadHelper.java

@@ -110,6 +110,7 @@ public final class DownloadHelper {
           DefaultTrackSelector.Parameters.DEFAULT_WITHOUT_CONTEXT
               .buildUpon()
               .setForceHighestSupportedBitrate(true)
+              .setConstrainAudioChannelCountToDeviceCapabilities(false)
               .build();
 
   /** Returns the default parameters used for track selection for downloading. */
@@ -117,6 +118,7 @@ public final class DownloadHelper {
     return DefaultTrackSelector.Parameters.getDefaults(context)
         .buildUpon()
         .setForceHighestSupportedBitrate(true)
+        .setConstrainAudioChannelCountToDeviceCapabilities(false)
         .build();
   }
 

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/trackselection/TrackSelector.java

@@ -17,7 +17,9 @@ package androidx.media3.exoplayer.trackselection;
 
 import static androidx.media3.common.util.Assertions.checkStateNotNull;
 
+import androidx.annotation.CallSuper;
 import androidx.annotation.Nullable;
+import androidx.media3.common.AudioAttributes;
 import androidx.media3.common.Player;
 import androidx.media3.common.Timeline;
 import androidx.media3.common.TrackSelectionParameters;
@@ -112,7 +114,8 @@ public abstract class TrackSelector {
    *     it has previously made are no longer valid.
    * @param bandwidthMeter A bandwidth meter which can be used by track selections to select tracks.
    */
-  public final void init(InvalidationListener listener, BandwidthMeter bandwidthMeter) {
+  @CallSuper
+  public void init(InvalidationListener listener, BandwidthMeter bandwidthMeter) {
     this.listener = listener;
     this.bandwidthMeter = bandwidthMeter;
   }
@@ -121,9 +124,10 @@ public abstract class TrackSelector {
    * Called by the player to release the selector. The selector cannot be used until {@link
    * #init(InvalidationListener, BandwidthMeter)} is called again.
    */
-  public final void release() {
-    this.listener = null;
-    this.bandwidthMeter = null;
+  @CallSuper
+  public void release() {
+    listener = null;
+    bandwidthMeter = null;
   }
 
   /**
@@ -178,6 +182,11 @@ public abstract class TrackSelector {
     return false;
   }
 
+  /** Called by the player to set the {@link AudioAttributes} that will be used for playback. */
+  public void setAudioAttributes(AudioAttributes audioAttributes) {
+    // Default implementation is no-op.
+  }
+
   /**
    * Calls {@link InvalidationListener#onTrackSelectionsInvalidated()} to invalidate all previously
    * generated track selections.