Add SilenceMediaSource

Issue: #5735
PiperOrigin-RevId: 248745617

RELEASENOTES.md

@@ -8,8 +8,11 @@
   even if they are listed lower in the `MediaCodecList`.
   even if they are listed lower in the `MediaCodecList`.
 * CEA-608: Handle XDS and TEXT modes
 * CEA-608: Handle XDS and TEXT modes
   ([5807](https://github.com/google/ExoPlayer/pull/5807)).
   ([5807](https://github.com/google/ExoPlayer/pull/5807)).
-* Audio: fix an issue where not all audio was played out when the configuration
+* Audio:
+ * Fix an issue where not all audio was played out when the configuration
    for the underlying track was changing (e.g., at some period transitions).
    for the underlying track was changing (e.g., at some period transitions).
+ * Add `SilenceMediaSource` that can be used to play silence of a given
+   duration ([#5735](https://github.com/google/ExoPlayer/issues/5735)).
 * UI: Change playback controls toggle from touch down to touch up events
 * UI: Change playback controls toggle from touch down to touch up events
   ([#5784](https://github.com/google/ExoPlayer/issues/5784)).
   ([#5784](https://github.com/google/ExoPlayer/issues/5784)).
 * Add a workaround for broken raw audio decoding on Oppo R9
 * Add a workaround for broken raw audio decoding on Oppo R9

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

+/*
+ * Copyright (C) 2019 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 com.google.android.exoplayer2.source;
+
+import androidx.annotation.Nullable;
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.FormatHolder;
+import com.google.android.exoplayer2.SeekParameters;
+import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
+import com.google.android.exoplayer2.trackselection.TrackSelection;
+import com.google.android.exoplayer2.upstream.Allocator;
+import com.google.android.exoplayer2.upstream.TransferListener;
+import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.MimeTypes;
+import com.google.android.exoplayer2.util.Util;
+import java.util.ArrayList;
+import org.checkerframework.checker.nullness.compatqual.NullableType;
+
+/** Media source with a single period consisting of silent raw audio of a given duration. */
+public final class SilenceMediaSource extends BaseMediaSource {
+
+  private static final int SAMPLE_RATE_HZ = 44100;
+  @C.PcmEncoding private static final int ENCODING = C.ENCODING_PCM_16BIT;
+  private static final int CHANNEL_COUNT = 2;
+  private static final Format FORMAT =
+      Format.createAudioSampleFormat(
+          /* id=*/ null,
+          MimeTypes.AUDIO_RAW,
+          /* codecs= */ null,
+          /* bitrate= */ Format.NO_VALUE,
+          /* maxInputSize= */ Format.NO_VALUE,
+          CHANNEL_COUNT,
+          SAMPLE_RATE_HZ,
+          ENCODING,
+          /* initializationData= */ null,
+          /* drmInitData= */ null,
+          /* selectionFlags= */ 0,
+          /* language= */ null);
+  private static final byte[] SILENCE_SAMPLE =
+      new byte[Util.getPcmFrameSize(ENCODING, CHANNEL_COUNT) * 1024];
+
+  private final long durationUs;
+
+  /**
+   * Creates a new media source providing silent audio of the given duration.
+   *
+   * @param durationUs The duration of silent audio to output, in microseconds.
+   */
+  public SilenceMediaSource(long durationUs) {
+    Assertions.checkArgument(durationUs >= 0);
+    this.durationUs = durationUs;
+  }
+
+  @Override
+  public void prepareSourceInternal(@Nullable TransferListener mediaTransferListener) {
+    refreshSourceInfo(
+        new SinglePeriodTimeline(durationUs, /* isSeekable= */ true, /* isDynamic= */ false),
+        /* manifest= */ null);
+  }
+
+  @Override
+  public void maybeThrowSourceInfoRefreshError() {}
+
+  @Override
+  public MediaPeriod createPeriod(MediaPeriodId id, Allocator allocator, long startPositionUs) {
+    return new SilenceMediaPeriod(durationUs);
+  }
+
+  @Override
+  public void releasePeriod(MediaPeriod mediaPeriod) {}
+
+  @Override
+  public void releaseSourceInternal() {}
+
+  private static final class SilenceMediaPeriod implements MediaPeriod {
+
+    private static final TrackGroupArray TRACKS = new TrackGroupArray(new TrackGroup(FORMAT));
+
+    private final long durationUs;
+    private final ArrayList<SampleStream> sampleStreams;
+
+    public SilenceMediaPeriod(long durationUs) {
+      this.durationUs = durationUs;
+      sampleStreams = new ArrayList<>();
+    }
+
+    @Override
+    public void prepare(Callback callback, long positionUs) {
+      callback.onPrepared(/* mediaPeriod= */ this);
+    }
+
+    @Override
+    public void maybeThrowPrepareError() {}
+
+    @Override
+    public TrackGroupArray getTrackGroups() {
+      return TRACKS;
+    }
+
+    @Override
+    public long selectTracks(
+        @NullableType TrackSelection[] selections,
+        boolean[] mayRetainStreamFlags,
+        @NullableType SampleStream[] streams,
+        boolean[] streamResetFlags,
+        long positionUs) {
+      for (int i = 0; i < selections.length; i++) {
+        if (streams[i] != null && (selections[i] == null || !mayRetainStreamFlags[i])) {
+          sampleStreams.remove(streams[i]);
+          streams[i] = null;
+        }
+        if (streams[i] == null && selections[i] != null) {
+          SilenceSampleStream stream = new SilenceSampleStream(durationUs);
+          stream.seekTo(positionUs);
+          sampleStreams.add(stream);
+          streams[i] = stream;
+          streamResetFlags[i] = true;
+        }
+      }
+      return positionUs;
+    }
+
+    @Override
+    public void discardBuffer(long positionUs, boolean toKeyframe) {}
+
+    @Override
+    public long readDiscontinuity() {
+      return C.TIME_UNSET;
+    }
+
+    @Override
+    public long seekToUs(long positionUs) {
+      for (int i = 0; i < sampleStreams.size(); i++) {
+        ((SilenceSampleStream) sampleStreams.get(i)).seekTo(positionUs);
+      }
+      return positionUs;
+    }
+
+    @Override
+    public long getAdjustedSeekPositionUs(long positionUs, SeekParameters seekParameters) {
+      return positionUs;
+    }
+
+    @Override
+    public long getBufferedPositionUs() {
+      return C.TIME_END_OF_SOURCE;
+    }
+
+    @Override
+    public long getNextLoadPositionUs() {
+      return C.TIME_END_OF_SOURCE;
+    }
+
+    @Override
+    public boolean continueLoading(long positionUs) {
+      return false;
+    }
+
+    @Override
+    public void reevaluateBuffer(long positionUs) {}
+  }
+
+  private static final class SilenceSampleStream implements SampleStream {
+
+    private final long durationBytes;
+
+    private boolean sentFormat;
+    private long positionBytes;
+
+    public SilenceSampleStream(long durationUs) {
+      durationBytes = getAudioByteCount(durationUs);
+      seekTo(0);
+    }
+
+    public void seekTo(long positionUs) {
+      positionBytes = getAudioByteCount(positionUs);
+    }
+
+    @Override
+    public boolean isReady() {
+      return true;
+    }
+
+    @Override
+    public void maybeThrowError() {}
+
+    @Override
+    public int readData(
+        FormatHolder formatHolder, DecoderInputBuffer buffer, boolean formatRequired) {
+      if (!sentFormat || formatRequired) {
+        formatHolder.format = FORMAT;
+        sentFormat = true;
+        return C.RESULT_FORMAT_READ;
+      }
+
+      long bytesRemaining = durationBytes - positionBytes;
+      if (bytesRemaining == 0) {
+        buffer.addFlag(C.BUFFER_FLAG_END_OF_STREAM);
+        return C.RESULT_BUFFER_READ;
+      }
+
+      int bytesToWrite = (int) Math.min(SILENCE_SAMPLE.length, bytesRemaining);
+      buffer.ensureSpaceForWrite(bytesToWrite);
+      buffer.addFlag(C.BUFFER_FLAG_KEY_FRAME);
+      buffer.data.put(SILENCE_SAMPLE, /* offset= */ 0, bytesToWrite);
+      buffer.timeUs = getAudioPositionUs(positionBytes);
+      positionBytes += bytesToWrite;
+      return C.RESULT_BUFFER_READ;
+    }
+
+    @Override
+    public int skipData(long positionUs) {
+      long oldPositionBytes = positionBytes;
+      seekTo(positionUs);
+      return (int) ((positionBytes - oldPositionBytes) / SILENCE_SAMPLE.length);
+    }
+  }
+
+  private static long getAudioByteCount(long durationUs) {
+    long audioSampleCount = durationUs * SAMPLE_RATE_HZ / C.MICROS_PER_SECOND;
+    return Util.getPcmFrameSize(ENCODING, CHANNEL_COUNT) * audioSampleCount;
+  }
+
+  private static long getAudioPositionUs(long bytes) {
+    long audioSampleCount = bytes / Util.getPcmFrameSize(ENCODING, CHANNEL_COUNT);
+    return audioSampleCount * C.MICROS_PER_SECOND / SAMPLE_RATE_HZ;
+  }
+}