Fix DTS Express Audio Buffer Underflow Issue.

RELEASENOTES.md

@@ -11,6 +11,8 @@
         stays at its current behavior of `true`.
 *   Extractors:
 *   Audio:
+    *   Fix DTS Express audio buffer underflow issue
+        ([#650](https://github.com/androidx/media/pull/650)).
 *   Video:
 *   Text:
     *   Remove `ExoplayerCuesDecoder`. Text tracks with `sampleMimeType =

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

@@ -63,6 +63,11 @@ public class DefaultAudioTrackBufferSizeProvider
    */
   private static final int AC3_BUFFER_MULTIPLICATION_FACTOR = 2;
 
+  /**
+   * Default multiplication factor to apply to DTS Express passthrough buffer to avoid underruns.
+   */
+  private static final int DTSHD_BUFFER_MULTIPLICATION_FACTOR = 4;
+
   /** A builder to create {@link DefaultAudioTrackBufferSizeProvider} instances. */
   public static class Builder {
 
@@ -72,6 +77,7 @@ public static class Builder {
     private int passthroughBufferDurationUs;
     private int offloadBufferDurationUs;
     private int ac3BufferMultiplicationFactor;
+    private int dtshdBufferMultiplicationFactor;
 
     /** Creates a new builder. */
     public Builder() {
@@ -81,6 +87,7 @@ public Builder() {
       passthroughBufferDurationUs = PASSTHROUGH_BUFFER_DURATION_US;
       offloadBufferDurationUs = OFFLOAD_BUFFER_DURATION_US;
       ac3BufferMultiplicationFactor = AC3_BUFFER_MULTIPLICATION_FACTOR;
+      dtshdBufferMultiplicationFactor = DTSHD_BUFFER_MULTIPLICATION_FACTOR;
     }
 
     /**
@@ -143,6 +150,16 @@ public Builder setAc3BufferMultiplicationFactor(int ac3BufferMultiplicationFacto
       return this;
     }
 
+    /**
+     * Sets the multiplication factor to apply to the passthrough buffer for DTS-HD (DTS Express) to
+     * avoid underruns. Default is {@link #DTSHD_BUFFER_MULTIPLICATION_FACTOR}.
+     */
+    @CanIgnoreReturnValue
+    public Builder setDtshdBufferMultiplicationFactor(int dtshdBufferMultiplicationFactor) {
+      this.dtshdBufferMultiplicationFactor = dtshdBufferMultiplicationFactor;
+      return this;
+    }
+
     /** Build the {@link DefaultAudioTrackBufferSizeProvider}. */
     public DefaultAudioTrackBufferSizeProvider build() {
       return new DefaultAudioTrackBufferSizeProvider(this);
@@ -170,13 +187,20 @@ public DefaultAudioTrackBufferSizeProvider build() {
    */
   public final int ac3BufferMultiplicationFactor;
 
+  /**
+   * The multiplication factor to apply to DTS-HD (DTS Express) passthrough buffer to avoid
+   * underruns.
+   */
+  public final int dtshdBufferMultiplicationFactor;
+
   protected DefaultAudioTrackBufferSizeProvider(Builder builder) {
     minPcmBufferDurationUs = builder.minPcmBufferDurationUs;
     maxPcmBufferDurationUs = builder.maxPcmBufferDurationUs;
     pcmBufferMultiplicationFactor = builder.pcmBufferMultiplicationFactor;
     passthroughBufferDurationUs = builder.passthroughBufferDurationUs;
     offloadBufferDurationUs = builder.offloadBufferDurationUs;
     ac3BufferMultiplicationFactor = builder.ac3BufferMultiplicationFactor;
+    dtshdBufferMultiplicationFactor = builder.dtshdBufferMultiplicationFactor;
   }
 
   @Override
@@ -232,7 +256,13 @@ protected int getPassthroughBufferSizeInBytes(@C.Encoding int encoding, int bitr
     int bufferSizeUs = passthroughBufferDurationUs;
     if (encoding == C.ENCODING_AC3) {
       bufferSizeUs *= ac3BufferMultiplicationFactor;
+    } else if (encoding == C.ENCODING_DTS_HD) {
+      // DTS-HD (DTS Express) for streaming uses a frame size (number of audio samples per channel
+      // per frame) of 4096. This requires a higher multiple for the buffersize computation.
+      // Otherwise, there will be buffer underflow during DASH playback.
+      bufferSizeUs *= dtshdBufferMultiplicationFactor;
     }
+
     int byteRate =
         bitrate != Format.NO_VALUE
             ? divide(bitrate, 8, RoundingMode.CEILING)

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/audio/DefaultAudioTrackBufferSizeProviderDTSHDTest.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2023 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 androidx.media3.exoplayer.audio;
+
+import static androidx.media3.common.C.MICROS_PER_SECOND;
+import static androidx.media3.exoplayer.audio.DefaultAudioSink.OUTPUT_MODE_PASSTHROUGH;
+import static androidx.media3.exoplayer.audio.DefaultAudioTrackBufferSizeProvider.getMaximumEncodedRateBytesPerSecond;
+import static com.google.common.truth.Truth.assertThat;
+
+import androidx.media3.common.C;
+import androidx.media3.common.Format;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Tests for {@link DefaultAudioTrackBufferSizeProvider} DTS-HD (DTS Express) audio. */
+@RunWith(AndroidJUnit4.class)
+public class DefaultAudioTrackBufferSizeProviderDTSHDTest {
+
+  private static final DefaultAudioTrackBufferSizeProvider DEFAULT =
+      new DefaultAudioTrackBufferSizeProvider.Builder().build();
+
+  @Test
+  public void
+      getBufferSizeInBytes_passthroughDtshdAndNoBitrate_assumesMaxByteRateTimesMultiplicationFactor() {
+    int bufferSize =
+        DEFAULT.getBufferSizeInBytes(
+            /* minBufferSizeInBytes= */ 0,
+            /* encoding= */ C.ENCODING_DTS_HD,
+            /* outputMode= */ OUTPUT_MODE_PASSTHROUGH,
+            /* pcmFrameSize= */ 1,
+            /* sampleRate= */ 0,
+            /* bitrate= */ Format.NO_VALUE,
+            /* maxAudioTrackPlaybackSpeed= */ 1);
+
+    assertThat(bufferSize)
+        .isEqualTo(
+            durationUsToDtshdMaxBytes(DEFAULT.passthroughBufferDurationUs)
+                * DEFAULT.dtshdBufferMultiplicationFactor);
+  }
+
+  @Test
+  public void
+      getBufferSizeInBytes_passthroughDtshdAt384Kbits_isPassthroughBufferSizeTimesMultiplicationFactor() {
+    int bufferSize =
+        DEFAULT.getBufferSizeInBytes(
+            /* minBufferSizeInBytes= */ 0,
+            /* encoding= */ C.ENCODING_DTS_HD,
+            /* outputMode= */ OUTPUT_MODE_PASSTHROUGH,
+            /* pcmFrameSize= */ 1,
+            /* sampleRate= */ 0,
+            /* bitrate= */ 384_000,
+            /* maxAudioTrackPlaybackSpeed= */ 1);
+
+    // Default buffer duration 0.25s => 0.25 * 384000 / 8 = 12000
+    assertThat(bufferSize).isEqualTo(12000 * DEFAULT.dtshdBufferMultiplicationFactor);
+  }
+
+  private static int durationUsToDtshdMaxBytes(long durationUs) {
+    return (int)
+        (durationUs * getMaximumEncodedRateBytesPerSecond(C.ENCODING_DTS_HD) / MICROS_PER_SECOND);
+  }
+}