id3.js

/**
 * ID3 parser
 */
import {logger} from '../utils/logger';
//import Hex from '../utils/hex';

 class ID3 {

  constructor(data) {
    this._hasTimeStamp = false;
    var offset = 0, byte1,byte2,byte3,byte4,tagSize,endPos,header,len;
      do {
        header = this.readUTF(data,offset,3);
        offset+=3;
          // first check for ID3 header
          if (header === 'ID3') {
              // skip 24 bits
              offset += 3;
              // retrieve tag(s) length
              byte1 = data[offset++] & 0x7f;
              byte2 = data[offset++] & 0x7f;
              byte3 = data[offset++] & 0x7f;
              byte4 = data[offset++] & 0x7f;
              tagSize = (byte1 << 21) + (byte2 << 14) + (byte3 << 7) + byte4;
              endPos = offset + tagSize;
              //logger.log(`ID3 tag found, size/end: ${tagSize}/${endPos}`);

              // read ID3 tags
              this._parseID3Frames(data, offset,endPos);
              offset = endPos;
          } else if (header === '3DI') {
              // http://id3.org/id3v2.4.0-structure chapter 3.4.   ID3v2 footer
              offset += 7;
                  logger.log(`3DI footer found, end: ${offset}`);
          } else {
              offset -= 3;
              len = offset;
                  if (len) {
                      //logger.log(`ID3 len: ${len}`);
                      if (!this.hasTimeStamp) {
                          logger.warn('ID3 tag found, but no timestamp');
                      }
                      this._length = len;
                      this._payload = data.subarray(0,len);
                  }
              return;
          }
      } while (true);
  }

  readUTF(data,start,len) {

    var result = '',offset = start, end = start + len;
    do {
      result += String.fromCharCode(data[offset++]);
    } while(offset < end);
    return result;
  }

  _parseID3Frames(data,offset,endPos) {
    var tagId,tagLen,tagStart,tagFlags,timestamp;
    while(offset + 8 <= endPos) {
      tagId = this.readUTF(data,offset,4);
      offset +=4;

      tagLen = data[offset++] << 24 +
                data[offset++] << 16 +
                data[offset++] << 8 +
                data[offset++];

      tagFlags = data[offset++] << 8 +
                  data[offset++];

      tagStart = offset;
      //logger.log("ID3 tag id:" + tagId);
      switch(tagId) {
        case 'PRIV':
            //logger.log('parse frame:' + Hex.hexDump(data.subarray(offset,endPos)));
            // owner should be "com.apple.streaming.transportStreamTimestamp"
            if (this.readUTF(data,offset,44) === 'com.apple.streaming.transportStreamTimestamp') {
                offset+=44;
                // smelling even better ! we found the right descriptor
                // skip null character (string end) + 3 first bytes
                offset+= 4;

                // timestamp is 33 bit expressed as a big-endian eight-octet number, with the upper 31 bits set to zero.
                var pts33Bit  = data[offset++] & 0x1;
                this._hasTimeStamp = true;

                timestamp = ((data[offset++] << 23) +
                             (data[offset++] << 15) +
                             (data[offset++] <<  7) +
                             data[offset++]) /45;

                if (pts33Bit) {
                    timestamp   += 47721858.84; // 2^32 / 90
                }
                timestamp = Math.round(timestamp);
                logger.trace(`ID3 timestamp found: ${timestamp}`);
                this._timeStamp = timestamp;
            }
            break;
        default:
            break;
      }
    }
  }

  get hasTimeStamp() {
    return this._hasTimeStamp;
  }

  get timeStamp() {
    return this._timeStamp;
  }

  get length() {
    return this._length;
  }

  get payload() {
    return this._payload;
  }

}

export default ID3;