parse method

@override ParserTag parse(RandomAccessFile reader)

Implementation

@override
ParserTag parse(RandomAccessFile reader) {
  reader.setPositionSync(0);

  buffer = Buffer(randomAccessFile: reader);

  // first page : contains samplerate and bitrate
  // second page : contains the metadata
  // it may not contains all the metadata so we would have to get them later
  final pages = [
    _parseUniquePage(),
    _parseUniquePage(),
  ];

  VorbisMetadata m = VorbisMetadata();

  for (final page in pages) {
    final content = page.data;

    if (String.fromCharCodes(content.sublist(0, 8)) == "OpusHead") {
      m.sampleRate = getUint32LE(content.sublist(12, 16));
      m.bitrate = getUint32LE(content.sublist(13, 17));
    } else if (String.fromCharCodes(content.sublist(0, 8)) == "OpusTags") {
      _parseVorbisComment(content, 8, m);
    } else if (String.fromCharCodes(content.sublist(0, 7)) ==
        String.fromCharCodes(
            [0x03, 0x76, 0x6F, 0x72, 0x62, 0x69, 0x73])) // "\x03vorbis"
    {
      _parseVorbisComment(content, 7, m);
    } else if (String.fromCharCodes(content.sublist(0, 7)) ==
        String.fromCharCodes(
            [0x01, 0x76, 0x6F, 0x72, 0x62, 0x69, 0x73])) // "\x01vorbis"
    {
      m.sampleRate = getUint32LE(content.sublist(12, 16));
      m.bitrate = getUint32LE(content.sublist(20, 24));
    }
  }

  // we need the sample rate to calculate the duration
  // it's mandatory
  // we have X samples per second (the sample rate obvio)
  // and a page contains exactly X samples

  if ((m.duration == null || m.duration == Duration.zero) &&
      m.sampleRate != null) {
    OggPage? page;

    while (page?.headerType != 0x04) {
      page = _parseUniquePageHeader();
    }

    m.duration = Duration(
      seconds: (page!.granulePosition - pages.first.granulePosition) ~/
          m.sampleRate!,
    );
  }

  reader.closeSync();

  return m;
}