Add SilenceMediaSource

Issue: #5735
PiperOrigin-RevId: 248745617

RELEASENOTES.md

@@ -4,6 +4,8 @@
 
 * Add `ResolvingDataSource` for just-in-time resolution of `DataSpec`s
   ([#5779](https://github.com/google/ExoPlayer/issues/5779)).
+* Add `SilenceMediaSource` that can be used to play silence of a given
+  duration ([#5735](https://github.com/google/ExoPlayer/issues/5735)).
 * Subtitles:
   * CEA-608: Handle XDS and TEXT modes
     ([#5807](https://github.com/google/ExoPlayer/pull/5807)).

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

@@ -0,0 +1,242 @@
+/*
+ * 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;
+  }
+}