Java ExtractorInput.advancePeekPosition方法代码示例

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
@Override
public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
  byte[] scratch = new byte[14];
  input.peekFully(scratch, 0, 14);

  // Verify the PACK_START_CODE for the first 4 bytes
  if (PACK_START_CODE != (((scratch[0] & 0xFF) << 24) | ((scratch[1] & 0xFF) << 16)
      | ((scratch[2] & 0xFF) << 8) | (scratch[3] & 0xFF))) {
    return false;
  }
  // Verify the 01xxx1xx marker on the 5th byte
  if ((scratch[4] & 0xC4) != 0x44) {
    return false;
  }
  // Verify the xxxxx1xx marker on the 7th byte
  if ((scratch[6] & 0x04) != 0x04) {
    return false;
  }
  // Verify the xxxxx1xx marker on the 9th byte
  if ((scratch[8] & 0x04) != 0x04) {
    return false;
  }
  // Verify the xxxxxxx1 marker on the 10th byte
  if ((scratch[9] & 0x01) != 0x01) {
    return false;
  }
  // Verify the xxxxxx11 marker on the 13th byte
  if ((scratch[12] & 0x03) != 0x03) {
    return false;
  }
  // Read the stuffing length from the 14th byte (last 3 bits)
  int packStuffingLength = scratch[13] & 0x07;
  input.advancePeekPosition(packStuffingLength);
  // Now check that the next 3 bytes are the beginning of an MPEG start code
  input.peekFully(scratch, 0, 3);
  return (PACKET_START_CODE_PREFIX == (((scratch[0] & 0xFF) << 16) | ((scratch[1] & 0xFF) << 8)
      | (scratch[2] & 0xFF)));
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
@Override
public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
  // Check if file starts with "FLV" tag
  input.peekFully(scratch.data, 0, 3);
  scratch.setPosition(0);
  if (scratch.readUnsignedInt24() != FLV_TAG) {
    return false;
  }

  // Checking reserved flags are set to 0
  input.peekFully(scratch.data, 0, 2);
  scratch.setPosition(0);
  if ((scratch.readUnsignedShort() & 0xFA) != 0) {
    return false;
  }

  // Read data offset
  input.peekFully(scratch.data, 0, 4);
  scratch.setPosition(0);
  int dataOffset = scratch.readInt();

  input.resetPeekPosition();
  input.advancePeekPosition(dataOffset);

  // Checking first "previous tag size" is set to 0
  input.peekFully(scratch.data, 0, 4);
  scratch.setPosition(0);

  return scratch.readInt() == 0;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * Peeks ID3 data from the input, including gapless playback information.
 *
 * @param input The {@link ExtractorInput} from which data should be peeked.
 * @throws IOException If an error occurred peeking from the input.
 * @throws InterruptedException If the thread was interrupted.
 */
private void peekId3Data(ExtractorInput input) throws IOException, InterruptedException {
  int peekedId3Bytes = 0;
  while (true) {
    input.peekFully(scratch.data, 0, Id3Decoder.ID3_HEADER_LENGTH);
    scratch.setPosition(0);
    if (scratch.readUnsignedInt24() != Id3Decoder.ID3_TAG) {
      // Not an ID3 tag.
      break;
    }
    scratch.skipBytes(3); // Skip major version, minor version and flags.
    int framesLength = scratch.readSynchSafeInt();
    int tagLength = Id3Decoder.ID3_HEADER_LENGTH + framesLength;

    if (metadata == null) {
      byte[] id3Data = new byte[tagLength];
      System.arraycopy(scratch.data, 0, id3Data, 0, Id3Decoder.ID3_HEADER_LENGTH);
      input.peekFully(id3Data, Id3Decoder.ID3_HEADER_LENGTH, framesLength);
      // We need to parse enough ID3 metadata to retrieve any gapless playback information even
      // if ID3 metadata parsing is disabled.
      Id3Decoder.FramePredicate id3FramePredicate = (flags & FLAG_DISABLE_ID3_METADATA) != 0
          ? GaplessInfoHolder.GAPLESS_INFO_ID3_FRAME_PREDICATE : null;
      metadata = new Id3Decoder(id3FramePredicate).decode(id3Data, tagLength);
      if (metadata != null) {
        gaplessInfoHolder.setFromMetadata(metadata);
      }
    } else {
      input.advancePeekPosition(framesLength);
    }

    peekedId3Bytes += tagLength;
  }

  input.resetPeekPosition();
  input.advancePeekPosition(peekedId3Bytes);
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * Peeks data from the input and parses ID3 metadata.
 *
 * @param input The {@link ExtractorInput} from which data should be peeked.
 * @param out The {@link GaplessInfoHolder} to populate.
 * @throws IOException If an error occurred peeking from the input.
 * @throws InterruptedException If the thread was interrupted.
 */
public static void parseId3(ExtractorInput input, GaplessInfoHolder out)
    throws IOException, InterruptedException {
  ParsableByteArray scratch = new ParsableByteArray(10);
  int peekedId3Bytes = 0;
  while (true) {
    input.peekFully(scratch.data, 0, 10);
    scratch.setPosition(0);
    if (scratch.readUnsignedInt24() != ID3_TAG) {
      break;
    }

    int majorVersion = scratch.readUnsignedByte();
    int minorVersion = scratch.readUnsignedByte();
    int flags = scratch.readUnsignedByte();
    int length = scratch.readSynchSafeInt();
    if (!out.hasGaplessInfo() && canParseMetadata(majorVersion, minorVersion, flags, length)) {
      byte[] frame = new byte[length];
      input.peekFully(frame, 0, length);
      parseGaplessInfo(new ParsableByteArray(frame), majorVersion, flags, out);
    } else {
      input.advancePeekPosition(length);
    }

    peekedId3Bytes += 10 + length;
  }
  input.resetPeekPosition();
  input.advancePeekPosition(peekedId3Bytes);
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
@Override
public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
  // Skip any ID3 headers.
  ParsableByteArray scratch = new ParsableByteArray(10);
  ParsableBitArray scratchBits = new ParsableBitArray(scratch.data);
  int startPosition = 0;
  while (true) {
    input.peekFully(scratch.data, 0, 10);
    scratch.setPosition(0);
    if (scratch.readUnsignedInt24() != ID3_TAG) {
      break;
    }
    scratch.skipBytes(3);
    int length = scratch.readSynchSafeInt();
    startPosition += 10 + length;
    input.advancePeekPosition(length);
  }
  input.resetPeekPosition();
  input.advancePeekPosition(startPosition);

  // Try to find four or more consecutive AAC audio frames, exceeding the MPEG TS packet size.
  int headerPosition = startPosition;
  int validFramesSize = 0;
  int validFramesCount = 0;
  while (true) {
    input.peekFully(scratch.data, 0, 2);
    scratch.setPosition(0);
    int syncBytes = scratch.readUnsignedShort();
    if ((syncBytes & 0xFFF6) != 0xFFF0) {
      validFramesCount = 0;
      validFramesSize = 0;
      input.resetPeekPosition();
      if (++headerPosition - startPosition >= MAX_SNIFF_BYTES) {
        return false;
      }
      input.advancePeekPosition(headerPosition);
    } else {
      if (++validFramesCount >= 4 && validFramesSize > 188) {
        return true;
      }

      // Skip the frame.
      input.peekFully(scratch.data, 0, 4);
      scratchBits.setPosition(14);
      int frameSize = scratchBits.readBits(13);
      // Either the stream is malformed OR we're not parsing an ADTS stream.
      if (frameSize <= 6) {
        return false;
      }
      input.advancePeekPosition(frameSize - 6);
      validFramesSize += frameSize;
    }
  }
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
@Override
public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
  // Skip any ID3 headers.
  ParsableByteArray scratch = new ParsableByteArray(10);
  int startPosition = 0;
  while (true) {
    input.peekFully(scratch.data, 0, 10);
    scratch.setPosition(0);
    if (scratch.readUnsignedInt24() != ID3_TAG) {
      break;
    }
    scratch.skipBytes(3);
    int length = scratch.readSynchSafeInt();
    startPosition += 10 + length;
    input.advancePeekPosition(length);
  }
  input.resetPeekPosition();
  input.advancePeekPosition(startPosition);

  int headerPosition = startPosition;
  int validFramesCount = 0;
  while (true) {
    input.peekFully(scratch.data, 0, 5);
    scratch.setPosition(0);
    int syncBytes = scratch.readUnsignedShort();
    if (syncBytes != AC3_SYNC_WORD) {
      validFramesCount = 0;
      input.resetPeekPosition();
      if (++headerPosition - startPosition >= MAX_SNIFF_BYTES) {
        return false;
      }
      input.advancePeekPosition(headerPosition);
    } else {
      if (++validFramesCount >= 4) {
        return true;
      }
      int frameSize = Ac3Util.parseAc3SyncframeSize(scratch.data);
      if (frameSize == C.LENGTH_UNSET) {
        return false;
      }
      input.advancePeekPosition(frameSize - 5);
    }
  }
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * Peeks and returns a {@code WavHeader}.
 *
 * @param input Input stream to peek the WAV header from.
 * @throws ParserException If the input file is an incorrect RIFF WAV.
 * @throws IOException If peeking from the input fails.
 * @throws InterruptedException If interrupted while peeking from input.
 * @return A new {@code WavHeader} peeked from {@code input}, or null if the input is not a
 *     supported WAV format.
 */
public static WavHeader peek(ExtractorInput input) throws IOException, InterruptedException {
  Assertions.checkNotNull(input);

  // Allocate a scratch buffer large enough to store the format chunk.
  ParsableByteArray scratch = new ParsableByteArray(16);

  // Attempt to read the RIFF chunk.
  ChunkHeader chunkHeader = ChunkHeader.peek(input, scratch);
  if (chunkHeader.id != Util.getIntegerCodeForString("RIFF")) {
    return null;
  }

  input.peekFully(scratch.data, 0, 4);
  scratch.setPosition(0);
  int riffFormat = scratch.readInt();
  if (riffFormat != Util.getIntegerCodeForString("WAVE")) {
    Log.e(TAG, "Unsupported RIFF format: " + riffFormat);
    return null;
  }

  // Skip chunks until we find the format chunk.
  chunkHeader = ChunkHeader.peek(input, scratch);
  while (chunkHeader.id != Util.getIntegerCodeForString("fmt ")) {
    input.advancePeekPosition((int) chunkHeader.size);
    chunkHeader = ChunkHeader.peek(input, scratch);
  }

  Assertions.checkState(chunkHeader.size >= 16);
  input.peekFully(scratch.data, 0, 16);
  scratch.setPosition(0);
  int type = scratch.readLittleEndianUnsignedShort();
  int numChannels = scratch.readLittleEndianUnsignedShort();
  int sampleRateHz = scratch.readLittleEndianUnsignedIntToInt();
  int averageBytesPerSecond = scratch.readLittleEndianUnsignedIntToInt();
  int blockAlignment = scratch.readLittleEndianUnsignedShort();
  int bitsPerSample = scratch.readLittleEndianUnsignedShort();

  int expectedBlockAlignment = numChannels * bitsPerSample / 8;
  if (blockAlignment != expectedBlockAlignment) {
    throw new ParserException("Expected block alignment: " + expectedBlockAlignment + "; got: "
        + blockAlignment);
  }

  @C.PcmEncoding int encoding = Util.getPcmEncoding(bitsPerSample);
  if (encoding == C.ENCODING_INVALID) {
    Log.e(TAG, "Unsupported WAV bit depth: " + bitsPerSample);
    return null;
  }

  if (type != TYPE_PCM && type != TYPE_WAVE_FORMAT_EXTENSIBLE) {
    Log.e(TAG, "Unsupported WAV format type: " + type);
    return null;
  }

  // If present, skip extensionSize, validBitsPerSample, channelMask, subFormatGuid, ...
  input.advancePeekPosition((int) chunkHeader.size - 16);

  return new WavHeader(numChannels, sampleRateHz, averageBytesPerSecond, blockAlignment,
      bitsPerSample, encoding);
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
private static boolean sniffInternal(ExtractorInput input, boolean fragmented)
    throws IOException, InterruptedException {
  long inputLength = input.getLength();
  int bytesToSearch = (int) (inputLength == C.LENGTH_UNSET || inputLength > SEARCH_LENGTH
      ? SEARCH_LENGTH : inputLength);

  ParsableByteArray buffer = new ParsableByteArray(64);
  int bytesSearched = 0;
  boolean foundGoodFileType = false;
  boolean isFragmented = false;
  while (bytesSearched < bytesToSearch) {
    // Read an atom header.
    int headerSize = Atom.HEADER_SIZE;
    buffer.reset(headerSize);
    input.peekFully(buffer.data, 0, headerSize);
    long atomSize = buffer.readUnsignedInt();
    int atomType = buffer.readInt();
    if (atomSize == Atom.LONG_SIZE_PREFIX) {
      headerSize = Atom.LONG_HEADER_SIZE;
      input.peekFully(buffer.data, Atom.HEADER_SIZE, Atom.LONG_HEADER_SIZE - Atom.HEADER_SIZE);
      buffer.setLimit(Atom.LONG_HEADER_SIZE);
      atomSize = buffer.readUnsignedLongToLong();
    }

    if (atomSize < headerSize) {
      // The file is invalid because the atom size is too small for its header.
      return false;
    }
    bytesSearched += headerSize;

    if (atomType == Atom.TYPE_moov) {
      // Check for an mvex atom inside the moov atom to identify whether the file is fragmented.
      continue;
    }

    if (atomType == Atom.TYPE_moof || atomType == Atom.TYPE_mvex) {
      // The movie is fragmented. Stop searching as we must have read any ftyp atom already.
      isFragmented = true;
      break;
    }

    if (bytesSearched + atomSize - headerSize >= bytesToSearch) {
      // Stop searching as peeking this atom would exceed the search limit.
      break;
    }

    int atomDataSize = (int) (atomSize - headerSize);
    bytesSearched += atomDataSize;
    if (atomType == Atom.TYPE_ftyp) {
      // Parse the atom and check the file type/brand is compatible with the extractors.
      if (atomDataSize < 8) {
        return false;
      }
      buffer.reset(atomDataSize);
      input.peekFully(buffer.data, 0, atomDataSize);
      int brandsCount = atomDataSize / 4;
      for (int i = 0; i < brandsCount; i++) {
        if (i == 1) {
          // This index refers to the minorVersion, not a brand, so skip it.
          buffer.skipBytes(4);
        } else if (isCompatibleBrand(buffer.readInt())) {
          foundGoodFileType = true;
          break;
        }
      }
      if (!foundGoodFileType) {
        // The types were not compatible and there is only one ftyp atom, so reject the file.
        return false;
      }
    } else if (atomDataSize != 0) {
      // Skip the atom.
      input.advancePeekPosition(atomDataSize);
    }
  }
  return foundGoodFileType && fragmented == isFragmented;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * @see com.google.android.exoplayer2.extractor.Extractor#sniff(ExtractorInput)
 */
public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
  long inputLength = input.getLength();
  int bytesToSearch = (int) (inputLength == C.LENGTH_UNSET || inputLength > SEARCH_LENGTH
      ? SEARCH_LENGTH : inputLength);
  // Find four bytes equal to ID_EBML near the start of the input.
  input.peekFully(scratch.data, 0, 4);
  long tag = scratch.readUnsignedInt();
  peekLength = 4;
  while (tag != ID_EBML) {
    if (++peekLength == bytesToSearch) {
      return false;
    }
    input.peekFully(scratch.data, 0, 1);
    tag = (tag << 8) & 0xFFFFFF00;
    tag |= scratch.data[0] & 0xFF;
  }

  // Read the size of the EBML header and make sure it is within the stream.
  long headerSize = readUint(input);
  long headerStart = peekLength;
  if (headerSize == Long.MIN_VALUE
      || (inputLength != C.LENGTH_UNSET && headerStart + headerSize >= inputLength)) {
    return false;
  }

  // Read the payload elements in the EBML header.
  while (peekLength < headerStart + headerSize) {
    long id = readUint(input);
    if (id == Long.MIN_VALUE) {
      return false;
    }
    long size = readUint(input);
    if (size < 0 || size > Integer.MAX_VALUE) {
      return false;
    }
    if (size != 0) {
      input.advancePeekPosition((int) size);
      peekLength += size;
    }
  }
  return peekLength == headerStart + headerSize;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
private boolean synchronize(ExtractorInput input, boolean sniffing)
    throws IOException, InterruptedException {
  int validFrameCount = 0;
  int candidateSynchronizedHeaderData = 0;
  int peekedId3Bytes = 0;
  int searchedBytes = 0;
  int searchLimitBytes = sniffing ? MAX_SNIFF_BYTES : MAX_SYNC_BYTES;
  input.resetPeekPosition();
  if (input.getPosition() == 0) {
    peekId3Data(input);
    peekedId3Bytes = (int) input.getPeekPosition();
    if (!sniffing) {
      input.skipFully(peekedId3Bytes);
    }
  }
  while (true) {
    if (!input.peekFully(scratch.data, 0, 4, validFrameCount > 0)) {
      // We reached the end of the stream but found at least one valid frame.
      break;
    }
    scratch.setPosition(0);
    int headerData = scratch.readInt();
    int frameSize;
    if ((candidateSynchronizedHeaderData != 0
        && (headerData & HEADER_MASK) != (candidateSynchronizedHeaderData & HEADER_MASK))
        || (frameSize = MpegAudioHeader.getFrameSize(headerData)) == C.LENGTH_UNSET) {
      // The header doesn't match the candidate header or is invalid. Try the next byte offset.
      if (searchedBytes++ == searchLimitBytes) {
        if (!sniffing) {
          throw new ParserException("Searched too many bytes.");
        }
        return false;
      }
      validFrameCount = 0;
      candidateSynchronizedHeaderData = 0;
      if (sniffing) {
        input.resetPeekPosition();
        input.advancePeekPosition(peekedId3Bytes + searchedBytes);
      } else {
        input.skipFully(1);
      }
    } else {
      // The header matches the candidate header and/or is valid.
      validFrameCount++;
      if (validFrameCount == 1) {
        MpegAudioHeader.populateHeader(headerData, synchronizedHeader);
        candidateSynchronizedHeaderData = headerData;
      } else if (validFrameCount == 4) {
        break;
      }
      input.advancePeekPosition(frameSize - 4);
    }
  }
  // Prepare to read the synchronized frame.
  if (sniffing) {
    input.skipFully(peekedId3Bytes + searchedBytes);
  } else {
    input.resetPeekPosition();
  }
  synchronizedHeaderData = candidateSynchronizedHeaderData;
  return true;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * Returns a {@link Seeker} to seek using metadata read from {@code input}, which should provide
 * data from the start of the first frame in the stream. On returning, the input's position will
 * be set to the start of the first frame of audio.
 *
 * @param input The {@link ExtractorInput} from which to read.
 * @throws IOException Thrown if there was an error reading from the stream. Not expected if the
 *     next two frames were already peeked during synchronization.
 * @throws InterruptedException Thrown if reading from the stream was interrupted. Not expected if
 *     the next two frames were already peeked during synchronization.
 * @return a {@link Seeker}.
 */
private Seeker setupSeeker(ExtractorInput input) throws IOException, InterruptedException {
  // Read the first frame which may contain a Xing or VBRI header with seeking metadata.
  ParsableByteArray frame = new ParsableByteArray(synchronizedHeader.frameSize);
  input.peekFully(frame.data, 0, synchronizedHeader.frameSize);

  long position = input.getPosition();
  long length = input.getLength();
  int headerData = 0;
  Seeker seeker = null;

  // Check if there is a Xing header.
  int xingBase = (synchronizedHeader.version & 1) != 0
      ? (synchronizedHeader.channels != 1 ? 36 : 21) // MPEG 1
      : (synchronizedHeader.channels != 1 ? 21 : 13); // MPEG 2 or 2.5
  if (frame.limit() >= xingBase + 4) {
    frame.setPosition(xingBase);
    headerData = frame.readInt();
  }
  if (headerData == XING_HEADER || headerData == INFO_HEADER) {
    seeker = XingSeeker.create(synchronizedHeader, frame, position, length);
    if (seeker != null && !gaplessInfoHolder.hasGaplessInfo()) {
      // If there is a Xing header, read gapless playback metadata at a fixed offset.
      input.resetPeekPosition();
      input.advancePeekPosition(xingBase + 141);
      input.peekFully(scratch.data, 0, 3);
      scratch.setPosition(0);
      gaplessInfoHolder.setFromXingHeaderValue(scratch.readUnsignedInt24());
    }
    input.skipFully(synchronizedHeader.frameSize);
  } else if (frame.limit() >= 40) {
    // Check if there is a VBRI header.
    frame.setPosition(36); // MPEG audio header (4 bytes) + 32 bytes.
    headerData = frame.readInt();
    if (headerData == VBRI_HEADER) {
      seeker = VbriSeeker.create(synchronizedHeader, frame, position, length);
      input.skipFully(synchronizedHeader.frameSize);
    }
  }

  if (seeker == null || (!seeker.isSeekable()
      && (flags & FLAG_ENABLE_CONSTANT_BITRATE_SEEKING) != 0)) {
    // Repopulate the synchronized header in case we had to skip an invalid seeking header, which
    // would give an invalid CBR bitrate.
    input.resetPeekPosition();
    input.peekFully(scratch.data, 0, 4);
    scratch.setPosition(0);
    MpegAudioHeader.populateHeader(scratch.readInt(), synchronizedHeader);
    seeker = new ConstantBitrateSeeker(input.getPosition(), synchronizedHeader.bitrate, length);
  }

  return seeker;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * @see Extractor#sniff
 */
public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
  long inputLength = input.getLength();
  int bytesToSearch = (int) (inputLength == C.LENGTH_UNSET || inputLength > SEARCH_LENGTH
      ? SEARCH_LENGTH : inputLength);
  // Find four bytes equal to ID_EBML near the start of the input.
  input.peekFully(scratch.data, 0, 4);
  long tag = scratch.readUnsignedInt();
  peekLength = 4;
  while (tag != ID_EBML) {
    if (++peekLength == bytesToSearch) {
      return false;
    }
    input.peekFully(scratch.data, 0, 1);
    tag = (tag << 8) & 0xFFFFFF00;
    tag |= scratch.data[0] & 0xFF;
  }

  // Read the size of the EBML header and make sure it is within the stream.
  long headerSize = readUint(input);
  long headerStart = peekLength;
  if (headerSize == Long.MIN_VALUE
      || (inputLength != C.LENGTH_UNSET && headerStart + headerSize >= inputLength)) {
    return false;
  }

  // Read the payload elements in the EBML header.
  while (peekLength < headerStart + headerSize) {
    long id = readUint(input);
    if (id == Long.MIN_VALUE) {
      return false;
    }
    long size = readUint(input);
    if (size < 0 || size > Integer.MAX_VALUE) {
      return false;
    }
    if (size != 0) {
      input.advancePeekPosition((int) size);
      peekLength += size;
    }
  }
  return peekLength == headerStart + headerSize;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
private boolean synchronize(ExtractorInput input, boolean sniffing)
    throws IOException, InterruptedException {
  int validFrameCount = 0;
  int candidateSynchronizedHeaderData = 0;
  int peekedId3Bytes = 0;
  int searchedBytes = 0;
  int searchLimitBytes = sniffing ? MAX_SNIFF_BYTES : MAX_SYNC_BYTES;
  input.resetPeekPosition();
  if (input.getPosition() == 0) {
    Id3Util.parseId3(input, gaplessInfoHolder);
    peekedId3Bytes = (int) input.getPeekPosition();
    if (!sniffing) {
      input.skipFully(peekedId3Bytes);
    }
  }
  while (true) {
    if (!input.peekFully(scratch.data, 0, 4, validFrameCount > 0)) {
      // We reached the end of the stream but found at least one valid frame.
      break;
    }
    scratch.setPosition(0);
    int headerData = scratch.readInt();
    int frameSize;
    if ((candidateSynchronizedHeaderData != 0
        && (headerData & HEADER_MASK) != (candidateSynchronizedHeaderData & HEADER_MASK))
        || (frameSize = MpegAudioHeader.getFrameSize(headerData)) == C.LENGTH_UNSET) {
      // The header doesn't match the candidate header or is invalid. Try the next byte offset.
      if (searchedBytes++ == searchLimitBytes) {
        if (!sniffing) {
          throw new ParserException("Searched too many bytes.");
        }
        return false;
      }
      validFrameCount = 0;
      candidateSynchronizedHeaderData = 0;
      if (sniffing) {
        input.resetPeekPosition();
        input.advancePeekPosition(peekedId3Bytes + searchedBytes);
      } else {
        input.skipFully(1);
      }
    } else {
      // The header matches the candidate header and/or is valid.
      validFrameCount++;
      if (validFrameCount == 1) {
        MpegAudioHeader.populateHeader(headerData, synchronizedHeader);
        candidateSynchronizedHeaderData = headerData;
      } else if (validFrameCount == 4) {
        break;
      }
      input.advancePeekPosition(frameSize - 4);
    }
  }
  // Prepare to read the synchronized frame.
  if (sniffing) {
    input.skipFully(peekedId3Bytes + searchedBytes);
  } else {
    input.resetPeekPosition();
  }
  synchronizedHeaderData = candidateSynchronizedHeaderData;
  return true;
}
 

import com.google.android.exoplayer2.extractor.ExtractorInput; //导入方法依赖的package包/类
/**
 * Returns a {@link Seeker} to seek using metadata read from {@code input}, which should provide
 * data from the start of the first frame in the stream. On returning, the input's position will
 * be set to the start of the first frame of audio.
 *
 * @param input The {@link ExtractorInput} from which to read.
 * @throws IOException Thrown if there was an error reading from the stream. Not expected if the
 *     next two frames were already peeked during synchronization.
 * @throws InterruptedException Thrown if reading from the stream was interrupted. Not expected if
 *     the next two frames were already peeked during synchronization.
 * @return a {@link Seeker}.
 */
private Seeker setupSeeker(ExtractorInput input) throws IOException, InterruptedException {
  // Read the first frame which may contain a Xing or VBRI header with seeking metadata.
  ParsableByteArray frame = new ParsableByteArray(synchronizedHeader.frameSize);
  input.peekFully(frame.data, 0, synchronizedHeader.frameSize);

  long position = input.getPosition();
  long length = input.getLength();
  int headerData = 0;
  Seeker seeker = null;

  // Check if there is a Xing header.
  int xingBase = (synchronizedHeader.version & 1) != 0
      ? (synchronizedHeader.channels != 1 ? 36 : 21) // MPEG 1
      : (synchronizedHeader.channels != 1 ? 21 : 13); // MPEG 2 or 2.5
  if (frame.limit() >= xingBase + 4) {
    frame.setPosition(xingBase);
    headerData = frame.readInt();
  }
  if (headerData == XING_HEADER || headerData == INFO_HEADER) {
    seeker = XingSeeker.create(synchronizedHeader, frame, position, length);
    if (seeker != null && !gaplessInfoHolder.hasGaplessInfo()) {
      // If there is a Xing header, read gapless playback metadata at a fixed offset.
      input.resetPeekPosition();
      input.advancePeekPosition(xingBase + 141);
      input.peekFully(scratch.data, 0, 3);
      scratch.setPosition(0);
      gaplessInfoHolder.setFromXingHeaderValue(scratch.readUnsignedInt24());
    }
    input.skipFully(synchronizedHeader.frameSize);
  } else if (frame.limit() >= 40) {
    // Check if there is a VBRI header.
    frame.setPosition(36); // MPEG audio header (4 bytes) + 32 bytes.
    headerData = frame.readInt();
    if (headerData == VBRI_HEADER) {
      seeker = VbriSeeker.create(synchronizedHeader, frame, position, length);
      input.skipFully(synchronizedHeader.frameSize);
    }
  }

  if (seeker == null) {
    // Repopulate the synchronized header in case we had to skip an invalid seeking header, which
    // would give an invalid CBR bitrate.
    input.resetPeekPosition();
    input.peekFully(scratch.data, 0, 4);
    scratch.setPosition(0);
    MpegAudioHeader.populateHeader(scratch.readInt(), synchronizedHeader);
    seeker = new ConstantBitrateSeeker(input.getPosition(), synchronizedHeader.bitrate, length);
  }

  return seeker;
}