Limit dynamic scheduling interval by the audio track buffer size

In certain bluetooth playback scenarios, it was found that the delta of audio duration written by the AudioSink from the current playback position was greater than the size of the audio track buffer, causing underruns.

The solution is to utilize the audio track buffer size as an upper limit for an audio renderer's getDurationToProgress.

PiperOrigin-RevId: 735761604

Author: microkatz

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/audio/AudioSink.java

@@ -591,6 +591,15 @@ default void setPreferredDevice(@Nullable AudioDeviceInfo audioDeviceInfo) {}
    */
   default void setOutputStreamOffsetUs(long outputStreamOffsetUs) {}
 
+  /**
+   * Returns the size of the underlying {@link AudioTrack} buffer in microseconds. If unsupported or
+   * the {@link AudioTrack} is not initialized then return {@link C#TIME_UNSET};
+   *
+   * <p>If the {@link AudioTrack} is configured with a compressed encoding, then the returned
+   * duration is an estimated minimum based on the encoding's maximum encoded byte rate.
+   */
+  long getAudioTrackBufferSizeUs();
+
   /**
    * Enables tunneling, if possible. The sink is reset if tunneling was previously disabled.
    * Enabling tunneling is only possible if the sink is based on a platform {@link AudioTrack}, and

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/audio/DecoderAudioRenderer.java

@@ -22,6 +22,7 @@
 import static androidx.media3.exoplayer.source.SampleStream.FLAG_REQUIRE_FORMAT;
 import static com.google.common.base.MoreObjects.firstNonNull;
 import static java.lang.Math.max;
+import static java.lang.Math.min;
 import static java.lang.annotation.ElementType.TYPE_USE;
 
 import android.media.AudioDeviceInfo;
@@ -246,16 +247,23 @@ public long getDurationToProgressUs(long positionUs, long elapsedRealtimeUs) {
     if (nextBufferToWritePresentationTimeUs == C.TIME_UNSET) {
       return super.getDurationToProgressUs(positionUs, elapsedRealtimeUs);
     }
-    long durationUs =
+    // Compare written, yet-to-play content duration against the audio track buffer size.
+    long writtenDurationUs = (nextBufferToWritePresentationTimeUs - positionUs);
+    long audioTrackBufferDurationUs = audioSink.getAudioTrackBufferSizeUs();
+    long bufferedDurationUs =
+        audioTrackBufferDurationUs != C.TIME_UNSET
+            ? min(audioTrackBufferDurationUs, writtenDurationUs)
+            : writtenDurationUs;
+    bufferedDurationUs =
         (long)
-            ((nextBufferToWritePresentationTimeUs - positionUs)
+            (bufferedDurationUs
                 / (getPlaybackParameters() != null ? getPlaybackParameters().speed : 1.0f)
                 / 2);
     if (isStarted) {
       // Account for the elapsed time since the start of this iteration of the rendering loop.
-      durationUs -= Util.msToUs(getClock().elapsedRealtime()) - elapsedRealtimeUs;
+      bufferedDurationUs -= Util.msToUs(getClock().elapsedRealtime()) - elapsedRealtimeUs;
     }
-    return max(DEFAULT_DURATION_TO_PROGRESS_US, durationUs);
+    return max(DEFAULT_DURATION_TO_PROGRESS_US, bufferedDurationUs);
   }
 
   @Override

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/audio/DefaultAudioSink.java

@@ -71,6 +71,7 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.math.RoundingMode;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.util.ArrayDeque;
@@ -1454,6 +1455,23 @@ public void setPreferredDevice(@Nullable AudioDeviceInfo audioDeviceInfo) {
     }
   }
 
+  @Override
+  public long getAudioTrackBufferSizeUs() {
+    if (!isAudioTrackInitialized()) {
+      return C.TIME_UNSET;
+    }
+    if (Util.SDK_INT >= 23) {
+      return Api23.getAudioTrackBufferSizeUs(audioTrack, configuration);
+    }
+    long byteRate =
+        configuration.outputMode == OUTPUT_MODE_PCM
+            ? (long) configuration.outputSampleRate * configuration.outputPcmFrameSize
+            : DefaultAudioTrackBufferSizeProvider.getMaximumEncodedRateBytesPerSecond(
+                configuration.outputEncoding);
+    return Util.scaleLargeValue(
+        configuration.bufferSize, C.MICROS_PER_SECOND, byteRate, RoundingMode.DOWN);
+  }
+
   @Override
   public void enableTunnelingV21() {
     Assertions.checkState(externalAudioSessionIdProvided);
@@ -2365,6 +2383,18 @@ public static void setPreferredDeviceOnAudioTrack(
       audioTrack.setPreferredDevice(
           audioDeviceInfo == null ? null : audioDeviceInfo.audioDeviceInfo);
     }
+
+    public static long getAudioTrackBufferSizeUs(
+        AudioTrack audioTrack, Configuration configuration) {
+      return configuration.outputMode == OUTPUT_MODE_PCM
+          ? configuration.framesToDurationUs(audioTrack.getBufferSizeInFrames())
+          : Util.scaleLargeValue(
+              audioTrack.getBufferSizeInFrames(),
+              C.MICROS_PER_SECOND,
+              DefaultAudioTrackBufferSizeProvider.getMaximumEncodedRateBytesPerSecond(
+                  configuration.outputEncoding),
+              RoundingMode.DOWN);
+    }
   }
 
   @RequiresApi(31)

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/audio/ForwardingAudioSink.java

@@ -162,6 +162,11 @@ public void setOutputStreamOffsetUs(long outputStreamOffsetUs) {
     sink.setOutputStreamOffsetUs(outputStreamOffsetUs);
   }
 
+  @Override
+  public long getAudioTrackBufferSizeUs() {
+    return sink.getAudioTrackBufferSizeUs();
+  }
+
   @Override
   public void enableTunnelingV21() {
     sink.enableTunnelingV21();

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/audio/MediaCodecAudioRenderer.java

@@ -20,6 +20,7 @@
 import static androidx.media3.exoplayer.DecoderReuseEvaluation.REUSE_RESULT_NO;
 import static com.google.common.base.MoreObjects.firstNonNull;
 import static java.lang.Math.max;
+import static java.lang.Math.min;
 
 import android.annotation.SuppressLint;
 import android.content.Context;
@@ -518,20 +519,27 @@ public MediaClock getMediaClock() {
   @Override
   protected long getDurationToProgressUs(
       long positionUs, long elapsedRealtimeUs, boolean isOnBufferAvailableListenerRegistered) {
-    if (nextBufferToWritePresentationTimeUs != C.TIME_UNSET) {
-      long durationUs =
-          (long)
-              ((nextBufferToWritePresentationTimeUs - positionUs)
-                  / (getPlaybackParameters() != null ? getPlaybackParameters().speed : 1.0f)
-                  / 2);
-      if (isStarted) {
-        // Account for the elapsed time since the start of this iteration of the rendering loop.
-        durationUs -= Util.msToUs(getClock().elapsedRealtime()) - elapsedRealtimeUs;
-      }
-      return max(DEFAULT_DURATION_TO_PROGRESS_US, durationUs);
+    if (nextBufferToWritePresentationTimeUs == C.TIME_UNSET) {
+      return super.getDurationToProgressUs(
+          positionUs, elapsedRealtimeUs, isOnBufferAvailableListenerRegistered);
+    }
+    // Compare written, yet-to-play content duration against the audio track buffer size.
+    long writtenDurationUs = (nextBufferToWritePresentationTimeUs - positionUs);
+    long audioTrackBufferDurationUs = audioSink.getAudioTrackBufferSizeUs();
+    long bufferedDurationUs =
+        audioTrackBufferDurationUs != C.TIME_UNSET
+            ? min(audioTrackBufferDurationUs, writtenDurationUs)
+            : writtenDurationUs;
+    bufferedDurationUs =
+        (long)
+            (bufferedDurationUs
+                / (getPlaybackParameters() != null ? getPlaybackParameters().speed : 1.0f)
+                / 2);
+    if (isStarted) {
+      // Account for the elapsed time since the start of this iteration of the rendering loop.
+      bufferedDurationUs -= Util.msToUs(getClock().elapsedRealtime()) - elapsedRealtimeUs;
     }
-    return super.getDurationToProgressUs(
-        positionUs, elapsedRealtimeUs, isOnBufferAvailableListenerRegistered);
+    return max(DEFAULT_DURATION_TO_PROGRESS_US, bufferedDurationUs);
   }
 
   @Override