jtBaseApp/node_modules/mux.js/cjs/aac/utils.js

/**
 * mux.js
 *
 * Copyright (c) Brightcove
 * Licensed Apache-2.0 https://github.com/videojs/mux.js/blob/master/LICENSE
 *
 * Utilities to detect basic properties and metadata about Aac data.
 */
'use strict';

var ADTS_SAMPLING_FREQUENCIES = [96000, 88200, 64000, 48000, 44100, 32000, 24000, 22050, 16000, 12000, 11025, 8000, 7350];

var parseId3TagSize = function parseId3TagSize(header, byteIndex) {
  var returnSize = header[byteIndex + 6] << 21 | header[byteIndex + 7] << 14 | header[byteIndex + 8] << 7 | header[byteIndex + 9],
      flags = header[byteIndex + 5],
      footerPresent = (flags & 16) >> 4; // if we get a negative returnSize clamp it to 0

  returnSize = returnSize >= 0 ? returnSize : 0;

  if (footerPresent) {
    return returnSize + 20;
  }

  return returnSize + 10;
};

var getId3Offset = function getId3Offset(data, offset) {
  if (data.length - offset < 10 || data[offset] !== 'I'.charCodeAt(0) || data[offset + 1] !== 'D'.charCodeAt(0) || data[offset + 2] !== '3'.charCodeAt(0)) {
    return offset;
  }

  offset += parseId3TagSize(data, offset);
  return getId3Offset(data, offset);
}; // TODO: use vhs-utils


var isLikelyAacData = function isLikelyAacData(data) {
  var offset = getId3Offset(data, 0);
  return data.length >= offset + 2 && (data[offset] & 0xFF) === 0xFF && (data[offset + 1] & 0xF0) === 0xF0 && // verify that the 2 layer bits are 0, aka this
  // is not mp3 data but aac data.
  (data[offset + 1] & 0x16) === 0x10;
};

var parseSyncSafeInteger = function parseSyncSafeInteger(data) {
  return data[0] << 21 | data[1] << 14 | data[2] << 7 | data[3];
}; // return a percent-encoded representation of the specified byte range
// @see http://en.wikipedia.org/wiki/Percent-encoding


var percentEncode = function percentEncode(bytes, start, end) {
  var i,
      result = '';

  for (i = start; i < end; i++) {
    result += '%' + ('00' + bytes[i].toString(16)).slice(-2);
  }

  return result;
}; // return the string representation of the specified byte range,
// interpreted as ISO-8859-1.


var parseIso88591 = function parseIso88591(bytes, start, end) {
  return unescape(percentEncode(bytes, start, end)); // jshint ignore:line
};

var parseAdtsSize = function parseAdtsSize(header, byteIndex) {
  var lowThree = (header[byteIndex + 5] & 0xE0) >> 5,
      middle = header[byteIndex + 4] << 3,
      highTwo = header[byteIndex + 3] & 0x3 << 11;
  return highTwo | middle | lowThree;
};

var parseType = function parseType(header, byteIndex) {
  if (header[byteIndex] === 'I'.charCodeAt(0) && header[byteIndex + 1] === 'D'.charCodeAt(0) && header[byteIndex + 2] === '3'.charCodeAt(0)) {
    return 'timed-metadata';
  } else if (header[byteIndex] & 0xff === 0xff && (header[byteIndex + 1] & 0xf0) === 0xf0) {
    return 'audio';
  }

  return null;
};

var parseSampleRate = function parseSampleRate(packet) {
  var i = 0;

  while (i + 5 < packet.length) {
    if (packet[i] !== 0xFF || (packet[i + 1] & 0xF6) !== 0xF0) {
      // If a valid header was not found,  jump one forward and attempt to
      // find a valid ADTS header starting at the next byte
      i++;
      continue;
    }

    return ADTS_SAMPLING_FREQUENCIES[(packet[i + 2] & 0x3c) >>> 2];
  }

  return null;
};

var parseAacTimestamp = function parseAacTimestamp(packet) {
  var frameStart, frameSize, frame, frameHeader; // find the start of the first frame and the end of the tag

  frameStart = 10;

  if (packet[5] & 0x40) {
    // advance the frame start past the extended header
    frameStart += 4; // header size field

    frameStart += parseSyncSafeInteger(packet.subarray(10, 14));
  } // parse one or more ID3 frames
  // http://id3.org/id3v2.3.0#ID3v2_frame_overview


  do {
    // determine the number of bytes in this frame
    frameSize = parseSyncSafeInteger(packet.subarray(frameStart + 4, frameStart + 8));

    if (frameSize < 1) {
      return null;
    }

    frameHeader = String.fromCharCode(packet[frameStart], packet[frameStart + 1], packet[frameStart + 2], packet[frameStart + 3]);

    if (frameHeader === 'PRIV') {
      frame = packet.subarray(frameStart + 10, frameStart + frameSize + 10);

      for (var i = 0; i < frame.byteLength; i++) {
        if (frame[i] === 0) {
          var owner = parseIso88591(frame, 0, i);

          if (owner === 'com.apple.streaming.transportStreamTimestamp') {
            var d = frame.subarray(i + 1);
            var size = (d[3] & 0x01) << 30 | d[4] << 22 | d[5] << 14 | d[6] << 6 | d[7] >>> 2;
            size *= 4;
            size += d[7] & 0x03;
            return size;
          }

          break;
        }
      }
    }

    frameStart += 10; // advance past the frame header

    frameStart += frameSize; // advance past the frame body
  } while (frameStart < packet.byteLength);

  return null;
};

module.exports = {
  isLikelyAacData: isLikelyAacData,
  parseId3TagSize: parseId3TagSize,
  parseAdtsSize: parseAdtsSize,
  parseType: parseType,
  parseSampleRate: parseSampleRate,
  parseAacTimestamp: parseAacTimestamp
};