android-34/com/google/android/exoplayer2/extractor/ts/AdtsExtractor.java

/*
 * Copyright (C) 2016 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.extractor.ts;

import static com.google.android.exoplayer2.extractor.ts.TsPayloadReader.FLAG_DATA_ALIGNMENT_INDICATOR;
import static com.google.android.exoplayer2.metadata.id3.Id3Decoder.ID3_HEADER_LENGTH;
import static com.google.android.exoplayer2.metadata.id3.Id3Decoder.ID3_TAG;

import androidx.annotation.IntDef;
import com.google.android.exoplayer2.C;
import com.google.android.exoplayer2.ParserException;
import com.google.android.exoplayer2.PlaybackException;
import com.google.android.exoplayer2.Player;
import com.google.android.exoplayer2.extractor.ConstantBitrateSeekMap;
import com.google.android.exoplayer2.extractor.Extractor;
import com.google.android.exoplayer2.extractor.ExtractorInput;
import com.google.android.exoplayer2.extractor.ExtractorOutput;
import com.google.android.exoplayer2.extractor.ExtractorsFactory;
import com.google.android.exoplayer2.extractor.PositionHolder;
import com.google.android.exoplayer2.extractor.SeekMap;
import com.google.android.exoplayer2.extractor.ts.TsPayloadReader.TrackIdGenerator;
import com.google.android.exoplayer2.util.Assertions;
import com.google.android.exoplayer2.util.ParsableBitArray;
import com.google.android.exoplayer2.util.ParsableByteArray;
import java.io.EOFException;
import java.io.IOException;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
import org.checkerframework.checker.nullness.qual.RequiresNonNull;

/** Extracts data from AAC bit streams with ADTS framing. */
public final class AdtsExtractor implements Extractor {

  /** Factory for {@link AdtsExtractor} instances. */
  public static final ExtractorsFactory FACTORY = () -> new Extractor[] {new AdtsExtractor()};

  /**
   * Flags controlling the behavior of the extractor. Possible flag values are {@link
   * #FLAG_ENABLE_CONSTANT_BITRATE_SEEKING} and {@link
   * #FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS}.
   */
  @Documented
  @Retention(RetentionPolicy.SOURCE)
  @IntDef(
      flag = true,
      value = {FLAG_ENABLE_CONSTANT_BITRATE_SEEKING, FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS})
  public @interface Flags {}
  /**
   * Flag to force enable seeking using a constant bitrate assumption in cases where seeking would
   * otherwise not be possible.
   *
   * <p>Note that this approach may result in approximated stream duration and seek position that
   * are not precise, especially when the stream bitrate varies a lot.
   */
  public static final int FLAG_ENABLE_CONSTANT_BITRATE_SEEKING = 1;
  /**
   * Like {@link #FLAG_ENABLE_CONSTANT_BITRATE_SEEKING}, except that seeking is also enabled in
   * cases where the content length (and hence the duration of the media) is unknown. Application
   * code should ensure that requested seek positions are valid when using this flag, or be ready to
   * handle playback failures reported through {@link Player.Listener#onPlayerError} with {@link
   * PlaybackException#errorCode} set to {@link
   * PlaybackException#ERROR_CODE_IO_READ_POSITION_OUT_OF_RANGE}.
   *
   * <p>If this flag is set, then the behavior enabled by {@link
   * #FLAG_ENABLE_CONSTANT_BITRATE_SEEKING} is implicitly enabled as well.
   */
  public static final int FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS = 1 << 1;

  private static final int MAX_PACKET_SIZE = 2 * 1024;
  /**
   * The maximum number of bytes to search when sniffing, excluding the header, before giving up.
   * Frame sizes are represented by 13-bit fields, so expect a valid frame in the first 8192 bytes.
   */
  private static final int MAX_SNIFF_BYTES = 8 * 1024;
  /**
   * The maximum number of frames to use when calculating the average frame size for constant
   * bitrate seeking.
   */
  private static final int NUM_FRAMES_FOR_AVERAGE_FRAME_SIZE = 1000;

  private final @Flags int flags;

  private final AdtsReader reader;
  private final ParsableByteArray packetBuffer;
  private final ParsableByteArray scratch;
  private final ParsableBitArray scratchBits;

  private @MonotonicNonNull ExtractorOutput extractorOutput;

  private long firstSampleTimestampUs;
  private long firstFramePosition;
  private int averageFrameSize;
  private boolean hasCalculatedAverageFrameSize;
  private boolean startedPacket;
  private boolean hasOutputSeekMap;

  /** Creates a new extractor for ADTS bitstreams. */
  public AdtsExtractor() {
    this(/* flags= */ 0);
  }

  /**
   * Creates a new extractor for ADTS bitstreams.
   *
   * @param flags Flags that control the extractor's behavior.
   */
  public AdtsExtractor(@Flags int flags) {
    if ((flags & FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS) != 0) {
      flags |= FLAG_ENABLE_CONSTANT_BITRATE_SEEKING;
    }
    this.flags = flags;
    reader = new AdtsReader(true);
    packetBuffer = new ParsableByteArray(MAX_PACKET_SIZE);
    averageFrameSize = C.LENGTH_UNSET;
    firstFramePosition = C.POSITION_UNSET;
    // Allocate scratch space for an ID3 header. The same buffer is also used to read 4 byte values.
    scratch = new ParsableByteArray(ID3_HEADER_LENGTH);
    scratchBits = new ParsableBitArray(scratch.getData());
  }

  // Extractor implementation.

  @Override
  public boolean sniff(ExtractorInput input) throws IOException {
    // Skip any ID3 headers.
    int startPosition = peekId3Header(input);

    // Try to find four or more consecutive AAC audio frames, exceeding the MPEG TS packet size.
    int headerPosition = startPosition;
    int totalValidFramesSize = 0;
    int validFramesCount = 0;
    while (true) {
      input.peekFully(scratch.getData(), 0, 2);
      scratch.setPosition(0);
      int syncBytes = scratch.readUnsignedShort();
      if (!AdtsReader.isAdtsSyncWord(syncBytes)) {
        // We didn't find an ADTS sync word. Start searching again from one byte further into the
        // start of the stream.
        validFramesCount = 0;
        totalValidFramesSize = 0;
        headerPosition++;
        input.resetPeekPosition();
        input.advancePeekPosition(headerPosition);
      } else {
        if (++validFramesCount >= 4 && totalValidFramesSize > TsExtractor.TS_PACKET_SIZE) {
          return true;
        }

        // Skip the frame.
        input.peekFully(scratch.getData(), 0, 4);
        scratchBits.setPosition(14);
        int frameSize = scratchBits.readBits(13);
        if (frameSize <= 6) {
          // The size is too small, so we're probably not reading an ADTS frame. Start searching
          // again from one byte further into the start of the stream.
          validFramesCount = 0;
          totalValidFramesSize = 0;
          headerPosition++;
          input.resetPeekPosition();
          input.advancePeekPosition(headerPosition);
        } else {
          input.advancePeekPosition(frameSize - 6);
          totalValidFramesSize += frameSize;
        }
      }
      if (headerPosition - startPosition >= MAX_SNIFF_BYTES) {
        return false;
      }
    }
  }

  @Override
  public void init(ExtractorOutput output) {
    this.extractorOutput = output;
    reader.createTracks(output, new TrackIdGenerator(0, 1));
    output.endTracks();
  }

  @Override
  public void seek(long position, long timeUs) {
    startedPacket = false;
    reader.seek();
    firstSampleTimestampUs = timeUs;
  }

  @Override
  public void release() {
    // Do nothing
  }

  @Override
  public int read(ExtractorInput input, PositionHolder seekPosition) throws IOException {
    Assertions.checkStateNotNull(extractorOutput); // Asserts that init has been called.

    long inputLength = input.getLength();
    boolean canUseConstantBitrateSeeking =
        (flags & FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS) != 0
            || ((flags & FLAG_ENABLE_CONSTANT_BITRATE_SEEKING) != 0
                && inputLength != C.LENGTH_UNSET);
    if (canUseConstantBitrateSeeking) {
      calculateAverageFrameSize(input);
    }

    int bytesRead = input.read(packetBuffer.getData(), 0, MAX_PACKET_SIZE);
    boolean readEndOfStream = bytesRead == RESULT_END_OF_INPUT;
    maybeOutputSeekMap(inputLength, readEndOfStream);
    if (readEndOfStream) {
      return RESULT_END_OF_INPUT;
    }

    // Feed whatever data we have to the reader, regardless of whether the read finished or not.
    packetBuffer.setPosition(0);
    packetBuffer.setLimit(bytesRead);

    if (!startedPacket) {
      // Pass data to the reader as though it's contained within a single infinitely long packet.
      reader.packetStarted(firstSampleTimestampUs, FLAG_DATA_ALIGNMENT_INDICATOR);
      startedPacket = true;
    }
    // TODO: Make it possible for reader to consume the dataSource directly, so that it becomes
    // unnecessary to copy the data through packetBuffer.
    reader.consume(packetBuffer);
    return RESULT_CONTINUE;
  }

  private int peekId3Header(ExtractorInput input) throws IOException {
    int firstFramePosition = 0;
    while (true) {
      input.peekFully(scratch.getData(), /* offset= */ 0, ID3_HEADER_LENGTH);
      scratch.setPosition(0);
      if (scratch.readUnsignedInt24() != ID3_TAG) {
        break;
      }
      scratch.skipBytes(3);
      int length = scratch.readSynchSafeInt();
      firstFramePosition += ID3_HEADER_LENGTH + length;
      input.advancePeekPosition(length);
    }
    input.resetPeekPosition();
    input.advancePeekPosition(firstFramePosition);
    if (this.firstFramePosition == C.POSITION_UNSET) {
      this.firstFramePosition = firstFramePosition;
    }
    return firstFramePosition;
  }

  @RequiresNonNull("extractorOutput")
  private void maybeOutputSeekMap(long inputLength, boolean readEndOfStream) {
    if (hasOutputSeekMap) {
      return;
    }

    boolean useConstantBitrateSeeking =
        (flags & FLAG_ENABLE_CONSTANT_BITRATE_SEEKING) != 0 && averageFrameSize > 0;
    if (useConstantBitrateSeeking
        && reader.getSampleDurationUs() == C.TIME_UNSET
        && !readEndOfStream) {
      // Wait for the sampleDurationUs to be available, or for the end of the stream to be reached,
      // before creating seek map.
      return;
    }

    if (useConstantBitrateSeeking && reader.getSampleDurationUs() != C.TIME_UNSET) {
      extractorOutput.seekMap(
          getConstantBitrateSeekMap(
              inputLength, (flags & FLAG_ENABLE_CONSTANT_BITRATE_SEEKING_ALWAYS) != 0));
    } else {
      extractorOutput.seekMap(new SeekMap.Unseekable(C.TIME_UNSET));
    }
    hasOutputSeekMap = true;
  }

  private void calculateAverageFrameSize(ExtractorInput input) throws IOException {
    if (hasCalculatedAverageFrameSize) {
      return;
    }
    averageFrameSize = C.LENGTH_UNSET;
    input.resetPeekPosition();
    if (input.getPosition() == 0) {
      // Skip any ID3 headers.
      peekId3Header(input);
    }

    int numValidFrames = 0;
    long totalValidFramesSize = 0;
    try {
      while (input.peekFully(
          scratch.getData(), /* offset= */ 0, /* length= */ 2, /* allowEndOfInput= */ true)) {
        scratch.setPosition(0);
        int syncBytes = scratch.readUnsignedShort();
        if (!AdtsReader.isAdtsSyncWord(syncBytes)) {
          // Invalid sync byte pattern.
          // Constant bit-rate seeking will probably fail for this stream.
          numValidFrames = 0;
          break;
        } else {
          // Read the frame size.
          if (!input.peekFully(
              scratch.getData(), /* offset= */ 0, /* length= */ 4, /* allowEndOfInput= */ true)) {
            break;
          }
          scratchBits.setPosition(14);
          int currentFrameSize = scratchBits.readBits(13);
          // Either the stream is malformed OR we're not parsing an ADTS stream.
          if (currentFrameSize <= 6) {
            hasCalculatedAverageFrameSize = true;
            throw ParserException.createForMalformedContainer(
                "Malformed ADTS stream", /* cause= */ null);
          }
          totalValidFramesSize += currentFrameSize;
          if (++numValidFrames == NUM_FRAMES_FOR_AVERAGE_FRAME_SIZE) {
            break;
          }
          if (!input.advancePeekPosition(currentFrameSize - 6, /* allowEndOfInput= */ true)) {
            break;
          }
        }
      }
    } catch (EOFException e) {
      // We reached the end of the input during a peekFully() or advancePeekPosition() operation.
      // This is OK, it just means the input has an incomplete ADTS frame at the end. Ideally
      // ExtractorInput would allow these operations to encounter end-of-input without throwing an
      // exception [internal: b/145586657].
    }
    input.resetPeekPosition();
    if (numValidFrames > 0) {
      averageFrameSize = (int) (totalValidFramesSize / numValidFrames);
    } else {
      averageFrameSize = C.LENGTH_UNSET;
    }
    hasCalculatedAverageFrameSize = true;
  }

  private SeekMap getConstantBitrateSeekMap(long inputLength, boolean allowSeeksIfLengthUnknown) {
    int bitrate = getBitrateFromFrameSize(averageFrameSize, reader.getSampleDurationUs());
    return new ConstantBitrateSeekMap(
        inputLength, firstFramePosition, bitrate, averageFrameSize, allowSeeksIfLengthUnknown);
  }

  /**
   * Returns the stream bitrate, given a frame size and the duration of that frame in microseconds.
   *
   * @param frameSize The size of each frame in the stream.
   * @param durationUsPerFrame The duration of the given frame in microseconds.
   * @return The stream bitrate.
   */
  private static int getBitrateFromFrameSize(int frameSize, long durationUsPerFrame) {
    return (int) ((frameSize * C.BITS_PER_BYTE * C.MICROS_PER_SECOND) / durationUsPerFrame);
  }
}