Encapsulate Opus frames in Ogg during audio offload

PiperOrigin-RevId: 508053559

library/core/src/main/java/com/google/android/exoplayer2/audio/DefaultAudioSink.java

@@ -1686,7 +1686,7 @@ public final class DefaultAudioSink implements AudioSink {
             : (Ac3Util.parseTrueHdSyncframeAudioSampleCount(buffer, syncframeOffset)
             : (Ac3Util.parseTrueHdSyncframeAudioSampleCount(buffer, syncframeOffset)
                 * Ac3Util.TRUEHD_RECHUNK_SAMPLE_COUNT);
                 * Ac3Util.TRUEHD_RECHUNK_SAMPLE_COUNT);
       case C.ENCODING_OPUS:
       case C.ENCODING_OPUS:
-        return OpusUtil.parsePacketAudioSampleCount(buffer);
+        return OpusUtil.parseOggPacketAudioSampleCount(buffer);
       case C.ENCODING_PCM_16BIT:
       case C.ENCODING_PCM_16BIT:
       case C.ENCODING_PCM_16BIT_BIG_ENDIAN:
       case C.ENCODING_PCM_16BIT_BIG_ENDIAN:
       case C.ENCODING_PCM_24BIT:
       case C.ENCODING_PCM_24BIT:

library/core/src/main/java/com/google/android/exoplayer2/audio/OggOpusAudioPacketizer.java

+/*
+ * 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 com.google.android.exoplayer2.audio;
+
+import static com.google.android.exoplayer2.audio.AudioProcessor.EMPTY_BUFFER;
+import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
+
+import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
+import com.google.android.exoplayer2.util.Util;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/** A packetizer that encapsulates OPUS audio encodings in OGG packets. */
+public final class OggOpusAudioPacketizer {
+
+  /** ID Header and Comment Header pages are 0 and 1 respectively */
+  private static final int FIRST_AUDIO_SAMPLE_PAGE_SEQUENCE = 2;
+
+  private ByteBuffer outputBuffer;
+  private int pageSequenceNumber;
+  private int granulePosition;
+
+  /** Creates an instance. */
+  public OggOpusAudioPacketizer() {
+    outputBuffer = EMPTY_BUFFER;
+    granulePosition = 0;
+    pageSequenceNumber = FIRST_AUDIO_SAMPLE_PAGE_SEQUENCE;
+  }
+
+  /**
+   * Packetizes the audio data between the position and limit of the {@code inputBuffer}.
+   *
+   * @param inputBuffer The input buffer to packetize. It must be a direct {@link ByteBuffer} with
+   *     LITTLE_ENDIAN order. The contents will be overwritten with the Ogg packet. The caller
+   *     retains ownership of the provided buffer.
+   */
+  public void packetize(DecoderInputBuffer inputBuffer) {
+    checkNotNull(inputBuffer.data);
+    if (inputBuffer.data.limit() - inputBuffer.data.position() == 0) {
+      return;
+    }
+    outputBuffer = packetizeInternal(inputBuffer.data);
+    inputBuffer.clear();
+    inputBuffer.ensureSpaceForWrite(outputBuffer.remaining());
+    inputBuffer.data.put(outputBuffer);
+    inputBuffer.flip();
+  }
+
+  /** Resets the packetizer. */
+  public void reset() {
+    outputBuffer = EMPTY_BUFFER;
+    granulePosition = 0;
+    pageSequenceNumber = FIRST_AUDIO_SAMPLE_PAGE_SEQUENCE;
+  }
+
+  /**
+   * Fill outputBuffer with an Ogg packet encapsulating the inputBuffer.
+   *
+   * @param inputBuffer contains Opus to wrap in Ogg packet
+   * @return {@link ByteBuffer} containing Ogg packet
+   */
+  private ByteBuffer packetizeInternal(ByteBuffer inputBuffer) {
+    int position = inputBuffer.position();
+    int limit = inputBuffer.limit();
+    int inputBufferSize = limit - position;
+
+    // inputBufferSize divisible by 255 requires extra '0' terminating lacing value
+    int numSegments = (inputBufferSize + 255) / 255;
+    int headerSize = 27 + numSegments;
+
+    int outputPacketSize = headerSize + inputBufferSize;
+
+    // Resample the little endian input and update the output buffers.
+    ByteBuffer buffer = replaceOutputBuffer(outputPacketSize);
+
+    // Capture Pattern for Page [OggS]
+    buffer.put((byte) 'O');
+    buffer.put((byte) 'g');
+    buffer.put((byte) 'g');
+    buffer.put((byte) 'S');
+
+    // StreamStructure Version
+    buffer.put((byte) 0);
+
+    // header_type_flag
+    buffer.put((byte) 0x00);
+
+    // granule_position
+    int numSamples = OpusUtil.parsePacketAudioSampleCount(inputBuffer);
+    granulePosition += numSamples;
+    buffer.putLong(granulePosition);
+
+    // bitstream_serial_number
+    buffer.putInt(0);
+
+    // page_sequence_number
+    buffer.putInt(pageSequenceNumber);
+    pageSequenceNumber++;
+
+    // CRC_checksum
+    buffer.putInt(0);
+
+    // number_page_segments
+    buffer.put((byte) numSegments);
+
+    // Segment_table
+    int bytesLeft = inputBufferSize;
+    for (int i = 0; i < numSegments; i++) {
+      if (bytesLeft >= 255) {
+        buffer.put((byte) 255);
+        bytesLeft -= 255;
+      } else {
+        buffer.put((byte) bytesLeft);
+        bytesLeft = 0;
+      }
+    }
+
+    for (int i = position; i < limit; i++) {
+      buffer.put(inputBuffer.get(i));
+    }
+
+    inputBuffer.position(inputBuffer.limit());
+    buffer.flip();
+
+    int checksum =
+        Util.crc32(
+            buffer.array(),
+            buffer.arrayOffset(),
+            buffer.limit() - buffer.position(),
+            /* initialValue= */ 0);
+    buffer.putInt(22, checksum);
+    buffer.position(0);
+
+    return buffer;
+  }
+
+  /**
+   * Replaces the current output buffer with a buffer of at least {@code size} bytes and returns it.
+   * Callers should write to the returned buffer then {@link ByteBuffer#flip()} it so it can be read
+   * via buffer.
+   */
+  private ByteBuffer replaceOutputBuffer(int size) {
+    if (outputBuffer.capacity() < size) {
+      outputBuffer = ByteBuffer.allocate(size).order(ByteOrder.LITTLE_ENDIAN);
+    } else {
+      outputBuffer.clear();
+    }
+    return outputBuffer;
+  }
+}

library/core/src/main/java/com/google/android/exoplayer2/mediacodec/MediaCodecRenderer.java

@@ -54,6 +54,7 @@ import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.FormatHolder;
 import com.google.android.exoplayer2.FormatHolder;
 import com.google.android.exoplayer2.PlaybackException;
 import com.google.android.exoplayer2.PlaybackException;
 import com.google.android.exoplayer2.analytics.PlayerId;
 import com.google.android.exoplayer2.analytics.PlayerId;
+import com.google.android.exoplayer2.audio.OggOpusAudioPacketizer;
 import com.google.android.exoplayer2.decoder.CryptoConfig;
 import com.google.android.exoplayer2.decoder.CryptoConfig;
 import com.google.android.exoplayer2.decoder.DecoderCounters;
 import com.google.android.exoplayer2.decoder.DecoderCounters;
 import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
 import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
@@ -307,6 +308,7 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
   private final long[] pendingOutputStreamStartPositionsUs;
   private final long[] pendingOutputStreamStartPositionsUs;
   private final long[] pendingOutputStreamOffsetsUs;
   private final long[] pendingOutputStreamOffsetsUs;
   private final long[] pendingOutputStreamSwitchTimesUs;
   private final long[] pendingOutputStreamSwitchTimesUs;
+  private final OggOpusAudioPacketizer oggOpusAudioPacketizer;
 
 
   @Nullable private Format inputFormat;
   @Nullable private Format inputFormat;
   @Nullable private Format outputFormat;
   @Nullable private Format outputFormat;
@@ -408,6 +410,7 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
     // endianness.
     // endianness.
     bypassBatchBuffer.ensureSpaceForWrite(/* length= */ 0);
     bypassBatchBuffer.ensureSpaceForWrite(/* length= */ 0);
     bypassBatchBuffer.data.order(ByteOrder.nativeOrder());
     bypassBatchBuffer.data.order(ByteOrder.nativeOrder());
+    oggOpusAudioPacketizer = new OggOpusAudioPacketizer();
 
 
     codecOperatingRate = CODEC_OPERATING_RATE_UNSET;
     codecOperatingRate = CODEC_OPERATING_RATE_UNSET;
     codecAdaptationWorkaroundMode = ADAPTATION_WORKAROUND_MODE_NEVER;
     codecAdaptationWorkaroundMode = ADAPTATION_WORKAROUND_MODE_NEVER;
@@ -726,6 +729,7 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
     bypassSampleBuffer.clear();
     bypassSampleBuffer.clear();
     bypassSampleBufferPending = false;
     bypassSampleBufferPending = false;
     bypassEnabled = false;
     bypassEnabled = false;
+    oggOpusAudioPacketizer.reset();
   }
   }
 
 
   protected void releaseCodec() {
   protected void releaseCodec() {
@@ -2311,6 +2315,13 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
           }
           }
           // Try to append the buffer to the batch buffer.
           // Try to append the buffer to the batch buffer.
           bypassSampleBuffer.flip();
           bypassSampleBuffer.flip();
+
+          if (inputFormat != null
+              && inputFormat.sampleMimeType != null
+              && inputFormat.sampleMimeType.equals(MimeTypes.AUDIO_OPUS)) {
+            oggOpusAudioPacketizer.packetize(bypassSampleBuffer);
+          }
+
           if (!bypassBatchBuffer.append(bypassSampleBuffer)) {
           if (!bypassBatchBuffer.append(bypassSampleBuffer)) {
             bypassSampleBufferPending = true;
             bypassSampleBufferPending = true;
             return;
             return;

library/core/src/test/java/com/google/android/exoplayer2/e2etest/OggOpusPlaybackTest.java

+/*
+ * Copyright (C) 2020 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.e2etest;
+
+import android.content.Context;
+import androidx.annotation.Nullable;
+import androidx.test.core.app.ApplicationProvider;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import com.google.android.exoplayer2.DefaultRenderersFactory;
+import com.google.android.exoplayer2.ExoPlayer;
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.MediaItem;
+import com.google.android.exoplayer2.Player;
+import com.google.android.exoplayer2.audio.AudioCapabilities;
+import com.google.android.exoplayer2.audio.AudioSink;
+import com.google.android.exoplayer2.audio.DefaultAudioSink;
+import com.google.android.exoplayer2.audio.ForwardingAudioSink;
+import com.google.android.exoplayer2.robolectric.ShadowMediaCodecConfig;
+import com.google.android.exoplayer2.robolectric.TestPlayerRunHelper;
+import com.google.android.exoplayer2.testutil.DumpFileAsserts;
+import com.google.android.exoplayer2.testutil.Dumper;
+import com.google.android.exoplayer2.testutil.FakeClock;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidJUnit4.class)
+public class OggOpusPlaybackTest {
+
+  public static final String INPUT_FILE = "bear.opus";
+
+  @Rule
+  public ShadowMediaCodecConfig mediaCodecConfig =
+      ShadowMediaCodecConfig.forAllSupportedMimeTypes();
+
+  @Test
+  public void checkOggOpusEncodings() throws Exception {
+    Context applicationContext = ApplicationProvider.getApplicationContext();
+    OffloadRenderersFactory offloadRenderersFactory =
+        new OffloadRenderersFactory(applicationContext);
+    ExoPlayer player =
+        new ExoPlayer.Builder(applicationContext, offloadRenderersFactory)
+            .setClock(new FakeClock(/* isAutoAdvancing= */ true))
+            .build();
+    player.setMediaItem(MediaItem.fromUri("asset:///media/ogg/" + INPUT_FILE));
+    player.prepare();
+    player.play();
+
+    TestPlayerRunHelper.runUntilPlaybackState(player, Player.STATE_ENDED);
+    player.release();
+
+    DumpFileAsserts.assertOutput(
+        applicationContext,
+        offloadRenderersFactory,
+        "playbackdumps/ogg/" + INPUT_FILE + ".oggOpus.dump");
+  }
+
+  private static class OffloadRenderersFactory extends DefaultRenderersFactory
+      implements Dumper.Dumpable {
+
+    private DumpingAudioSink dumpingAudioSink;
+
+    /**
+     * @param context A {@link Context}.
+     */
+    public OffloadRenderersFactory(Context context) {
+      super(context);
+      setEnableAudioOffload(true);
+    }
+
+    @Override
+    protected AudioSink buildAudioSink(
+        Context context,
+        boolean enableFloatOutput,
+        boolean enableAudioTrackPlaybackParams,
+        boolean enableOffload) {
+      dumpingAudioSink =
+          new DumpingAudioSink(
+              new DefaultAudioSink.Builder()
+                  .setAudioCapabilities(AudioCapabilities.getCapabilities(context))
+                  .setEnableFloatOutput(enableFloatOutput)
+                  .setEnableAudioTrackPlaybackParams(enableAudioTrackPlaybackParams)
+                  .setOffloadMode(DefaultAudioSink.OFFLOAD_MODE_ENABLED_GAPLESS_REQUIRED)
+                  .build());
+      return dumpingAudioSink;
+    }
+
+    @Override
+    public void dump(Dumper dumper) {
+      dumpingAudioSink.dump(dumper);
+    }
+  }
+
+  private static class DumpingAudioSink extends ForwardingAudioSink implements Dumper.Dumpable {
+    /** All handleBuffer interactions recorded with this audio sink. */
+    private final List<CapturedInputBuffer> capturedInteractions;
+
+    public DumpingAudioSink(AudioSink sink) {
+      super(sink);
+      capturedInteractions = new ArrayList<>();
+    }
+
+    @Override
+    public void configure(
+        Format inputFormat, int specifiedBufferSize, @Nullable int[] outputChannels)
+        throws ConfigurationException {
+      // Bypass configure of base DefaultAudioSink
+    }
+
+    @Override
+    public boolean supportsFormat(Format format) {
+      return true;
+    }
+
+    @Override
+    public boolean handleBuffer(
+        ByteBuffer buffer, long presentationTimeUs, int encodedAccessUnitCount)
+        throws InitializationException, WriteException {
+      capturedInteractions.add(
+          new CapturedInputBuffer(peekBytes(buffer, 0, buffer.limit() - buffer.position())));
+      return true;
+    }
+
+    @Override
+    public void dump(Dumper dumper) {
+      dumper.startBlock("SinkDump (OggOpus)");
+      dumper.add("buffers.length", capturedInteractions.size());
+      for (int i = 0; i < capturedInteractions.size(); i++) {
+        dumper.add("buffers[" + i + "]", capturedInteractions.get(i).contents);
+      }
+      dumper.endBlock();
+    }
+
+    private byte[] peekBytes(ByteBuffer buffer, int offset, int size) {
+      int originalPosition = buffer.position();
+      buffer.position(offset);
+      byte[] bytes = new byte[size];
+      buffer.get(bytes);
+      buffer.position(originalPosition);
+      return bytes;
+    }
+  }
+
+  /** Data record */
+  private static class CapturedInputBuffer {
+    private final byte[] contents;
+
+    private CapturedInputBuffer(byte[] contents) {
+      this.contents = contents;
+    }
+  }
+}

library/extractor/src/main/java/com/google/android/exoplayer2/audio/OpusUtil.java

@@ -65,6 +65,25 @@ public class OpusUtil {
   }
   }
 
 
   /**
   /**
+   * Returns the number of audio samples in the given Ogg encapuslated Opus packet.
+   *
+   * <p>The buffer's position is not modified.
+   *
+   * @param buffer The audio packet.
+   * @return Returns the number of audio samples in the packet.
+   */
+  public static int parseOggPacketAudioSampleCount(ByteBuffer buffer) {
+    // RFC 3433 section 6 - The Ogg page format.
+    int numPageSegments = buffer.get(/* index= */ 26);
+    int indexFirstOpusPacket = 27 + numPageSegments; // Skip Ogg header and segment table.
+    long packetDurationUs =
+        getPacketDurationUs(
+            buffer.get(indexFirstOpusPacket),
+            buffer.limit() > 1 ? buffer.get(indexFirstOpusPacket + 1) : 0);
+    return (int) (packetDurationUs * SAMPLE_RATE / C.MICROS_PER_SECOND);
+  }
+
+  /**
    * Returns the number of audio samples in the given audio packet.
    * Returns the number of audio samples in the given audio packet.
    *
    *
    * <p>The buffer's position is not modified.
    * <p>The buffer's position is not modified.

testdata/src/test/assets/playbackdumps/ogg/bear.opus.oggOpus.dump

+SinkDump (OggOpus):
+  buffers.length = 9
+  buffers[0] = length 4046, hash 68FA8318
+  buffers[1] = length 3848, hash B3105060
+  buffers[2] = length 3747, hash 63B6648B
+  buffers[3] = length 3752, hash B5C28B9D
+  buffers[4] = length 3776, hash AC7CEC0B
+  buffers[5] = length 3829, hash B64088F2
+  buffers[6] = length 3745, hash 1C46E49A
+  buffers[7] = length 3726, hash 2BC03F39
+  buffers[8] = length 2772, hash A6C7BB9

testutils/src/main/java/com/google/android/exoplayer2/testutil/OggFileAudioBufferSink.java

+/*
+ * 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 com.google.android.exoplayer2.testutil;
+
+import static java.lang.Math.min;
+
+import android.os.Environment;
+import androidx.annotation.Nullable;
+import com.google.android.exoplayer2.audio.AudioSink;
+import com.google.android.exoplayer2.audio.ForwardingAudioSink;
+import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.Log;
+import com.google.android.exoplayer2.util.Util;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+/**
+ * A sink for audio buffers that writes output audio as .ogg files with a given path prefix. When
+ * new audio data is handled after flushing the audio packetizer, a counter is incremented and its
+ * value is appended to the output file name.
+ *
+ * <p>Note: if writing to external storage it's necessary to grant the {@code
+ * WRITE_EXTERNAL_STORAGE} permission.
+ */
+public final class OggFileAudioBufferSink extends ForwardingAudioSink {
+
+  /** Opus streams are always 48000 Hz. */
+  public static final int SAMPLE_RATE = 48_000;
+
+  private static final String TAG = "OggFileAudioBufferSink";
+  private static final int OGG_ID_HEADER_LENGTH = 47;
+  private static final int OGG_COMMENT_HEADER_LENGTH = 52;
+
+  private final byte[] scratchBuffer;
+  private final ByteBuffer scratchByteBuffer;
+  private final String outputFileNamePrefix;
+
+  @Nullable private RandomAccessFile randomAccessFile;
+  private int counter;
+
+  /**
+   * Creates an instance.
+   *
+   * @param audioSink The base audioSink calls are forwarded to.
+   * @param outputFileNamePrefix The prefix for output files.
+   */
+  public OggFileAudioBufferSink(AudioSink audioSink, String outputFileNamePrefix) {
+    super(audioSink);
+    this.outputFileNamePrefix = outputFileNamePrefix;
+    counter = 0;
+    scratchBuffer = new byte[1024];
+    scratchByteBuffer = ByteBuffer.wrap(scratchBuffer).order(ByteOrder.LITTLE_ENDIAN);
+  }
+
+  @Override
+  public void flush() {
+    super.flush();
+    try {
+      resetInternal();
+    } catch (IOException e) {
+      Log.e(TAG, "Error resetting", e);
+    }
+  }
+
+  @Override
+  public void reset() {
+    super.reset();
+    try {
+      resetInternal();
+    } catch (IOException e) {
+      Log.e(TAG, "Error resetting", e);
+    }
+  }
+
+  @Override
+  public boolean handleBuffer(
+      ByteBuffer buffer, long presentationTimeUs, int encodedAccessUnitCount)
+      throws InitializationException, WriteException {
+    handleBuffer(buffer);
+    return super.handleBuffer(buffer, presentationTimeUs, encodedAccessUnitCount);
+  }
+
+  private void handleBuffer(ByteBuffer buffer) {
+    try {
+      maybePrepareFile();
+      writeBuffer(buffer);
+    } catch (IOException e) {
+      Log.e(TAG, "Error writing data", e);
+    }
+  }
+
+  private void maybePrepareFile() throws IOException {
+    if (randomAccessFile != null) {
+      return;
+    }
+    RandomAccessFile randomAccessFile = new RandomAccessFile(getNextOutputFileName(), "rw");
+    scratchByteBuffer.clear();
+    writeIdHeaderPacket();
+    writeCommentHeaderPacket();
+    randomAccessFile.write(scratchBuffer, 0, scratchByteBuffer.position());
+    this.randomAccessFile = randomAccessFile;
+  }
+
+  private void writeOggPacketHeader(int pageSequenceNumber, boolean isIdHeaderPacket) {
+    // Capture Pattern for Page [OggS]
+    scratchByteBuffer.put((byte) 'O');
+    scratchByteBuffer.put((byte) 'g');
+    scratchByteBuffer.put((byte) 'g');
+    scratchByteBuffer.put((byte) 'S');
+
+    // StreamStructure Version
+    scratchByteBuffer.put((byte) 0);
+
+    // header-type
+    scratchByteBuffer.put(isIdHeaderPacket ? (byte) 0x02 : (byte) 0x00);
+
+    // granule_position
+    scratchByteBuffer.putLong((long) 0);
+
+    // bitstream_serial_number
+    scratchByteBuffer.putInt(0);
+
+    // page_sequence_number
+    scratchByteBuffer.putInt(pageSequenceNumber);
+
+    // CRC_checksum
+    scratchByteBuffer.putInt(0);
+
+    // number_page_segments
+    scratchByteBuffer.put((byte) 1);
+  }
+
+  private void writeIdHeaderPacket() {
+    // Id Header
+    writeOggPacketHeader(/* pageSequenceNumber= */ 0, /* isIdHeaderPacket= */ true);
+
+    // Payload Size = 19
+    scratchByteBuffer.put((byte) 19);
+
+    // OggOpus Id Header Capture Pattern 8
+    scratchByteBuffer.put((byte) 'O');
+    scratchByteBuffer.put((byte) 'p');
+    scratchByteBuffer.put((byte) 'u');
+    scratchByteBuffer.put((byte) 's');
+    scratchByteBuffer.put((byte) 'H');
+    scratchByteBuffer.put((byte) 'e');
+    scratchByteBuffer.put((byte) 'a');
+    scratchByteBuffer.put((byte) 'd');
+
+    // version
+    scratchByteBuffer.put((byte) 1);
+
+    // output channel count
+    scratchByteBuffer.put((byte) 2);
+
+    // pre-skip
+    scratchByteBuffer.putShort((short) 312);
+
+    // input sample rate
+    scratchByteBuffer.putInt(SAMPLE_RATE);
+
+    // Output Gain
+    scratchByteBuffer.putShort((short) 0);
+
+    // channel mapping family
+    scratchByteBuffer.put((byte) 0);
+
+    int checksum =
+        Util.crc32(scratchBuffer, /* start= */ 0, OGG_ID_HEADER_LENGTH, /* initialValue= */ 0);
+    scratchByteBuffer.putInt(/* index= */ 22, checksum);
+    scratchByteBuffer.position(OGG_ID_HEADER_LENGTH);
+  }
+
+  private void writeCommentHeaderPacket() {
+    // Id Header
+    writeOggPacketHeader(/* pageSequenceNumber= */ 1, /* isIdHeaderPacket= */ false);
+
+    // Payload Size = 24
+    scratchByteBuffer.put((byte) 24);
+
+    // Comment Header Opus Capture Pattern 8
+    scratchByteBuffer.put((byte) 'O');
+    scratchByteBuffer.put((byte) 'p');
+    scratchByteBuffer.put((byte) 'u');
+    scratchByteBuffer.put((byte) 's');
+    scratchByteBuffer.put((byte) 'T');
+    scratchByteBuffer.put((byte) 'a');
+    scratchByteBuffer.put((byte) 'g');
+    scratchByteBuffer.put((byte) 's');
+
+    // Vendor Comment String Length
+    scratchByteBuffer.putInt(8);
+
+    // Vendor Comment String
+    scratchByteBuffer.put((byte) 'G');
+    scratchByteBuffer.put((byte) 'o');
+    scratchByteBuffer.put((byte) 'o');
+    scratchByteBuffer.put((byte) 'g');
+    scratchByteBuffer.put((byte) 'l');
+    scratchByteBuffer.put((byte) 'e');
+    scratchByteBuffer.put((byte) 'r');
+    scratchByteBuffer.put((byte) 's');
+
+    // UserCommentList Length
+    scratchByteBuffer.putInt(0);
+
+    int checksum =
+        Util.crc32(
+            scratchBuffer,
+            OGG_ID_HEADER_LENGTH,
+            OGG_ID_HEADER_LENGTH + OGG_COMMENT_HEADER_LENGTH,
+            /* initialValue= */ 0);
+
+    scratchByteBuffer.putInt(/* index= */ 69, checksum);
+
+    scratchByteBuffer.position(OGG_ID_HEADER_LENGTH + OGG_COMMENT_HEADER_LENGTH);
+  }
+
+  private void writeBuffer(ByteBuffer buffer) throws IOException {
+    RandomAccessFile randomAccessFile = Assertions.checkNotNull(this.randomAccessFile);
+    while (buffer.hasRemaining()) {
+      int bytesToWrite = min(buffer.remaining(), scratchBuffer.length);
+      buffer.get(scratchBuffer, /* offset= */ 0, bytesToWrite);
+      randomAccessFile.write(scratchBuffer, /* off= */ 0, bytesToWrite);
+    }
+  }
+
+  private void resetInternal() throws IOException {
+    @Nullable RandomAccessFile randomAccessFile = this.randomAccessFile;
+    if (randomAccessFile == null) {
+      return;
+    }
+
+    try {
+      randomAccessFile.close();
+    } finally {
+      this.randomAccessFile = null;
+    }
+  }
+
+  private String getNextOutputFileName() {
+    return Util.formatInvariant(
+        "%s/%s-%04d.ogg",
+        Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC)
+            .getAbsolutePath(),
+        outputFileNamePrefix,
+        counter++);
+  }
+}