# All files / src/demux adts.js

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100% Branches 51/51
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     /**
     * ADTS parser helper
     * @link https://wiki.multimedia.cx/index.php?title=ADTS
     */
    import { logger } from '../utils/logger';
    import { ErrorTypes, ErrorDetails } from '../errors';

    import Event from '../events';

    import { getSelfScope } from '../utils/get-self-scope';

    export function getAudioConfig (observer, data, offset, audioCodec) {
      let adtsObjectType, // :int
        adtsSampleingIndex, // :int
        adtsExtensionSampleingIndex, // :int
        adtsChanelConfig, // :int
        config,
        userAgent = navigator.userAgent.toLowerCase(),
        manifestCodec = audioCodec,
        adtsSampleingRates = [
          96000, 88200,
          64000, 48000,
          44100, 32000,
          24000, 22050,
          16000, 12000,
          11025, 8000,
          7350];
      // byte 2
      adtsObjectType = ((data[offset + 2] & 0xC0) >>> 6) + 1;
      adtsSampleingIndex = ((data[offset + 2] & 0x3C) >>> 2);
      if (adtsSampleingIndex > adtsSampleingRates.length - 1) {
        observer.trigger(Event.ERROR, { type: ErrorTypes.MEDIA_ERROR, details: ErrorDetails.FRAG_PARSING_ERROR, fatal: true, reason: `invalid ADTS sampling index:${adtsSampleingIndex}` });
        return;
      }
      adtsChanelConfig = ((data[offset + 2] & 0x01) << 2);
      // byte 3
      adtsChanelConfig |= ((data[offset + 3] & 0xC0) >>> 6);
      logger.log(`manifest codec:${audioCodec},ADTS data:type:${adtsObjectType},sampleingIndex:${adtsSampleingIndex}[${adtsSampleingRates[adtsSampleingIndex]}Hz],channelConfig:${adtsChanelConfig}`);
      // firefox: freq less than 24kHz = AAC SBR (HE-AAC)
      if (/firefox/i.test(userAgent)) {
        if (adtsSampleingIndex >= 6) {
          adtsObjectType = 5;
          config = new Array(4);
          // HE-AAC uses SBR (Spectral Band Replication) , high frequencies are constructed from low frequencies
          // there is a factor 2 between frame sample rate and output sample rate
          // multiply frequency by 2 (see table below, equivalent to substract 3)
          adtsExtensionSampleingIndex = adtsSampleingIndex - 3;
        } else {
          adtsObjectType = 2;
          config = new Array(2);
          adtsExtensionSampleingIndex = adtsSampleingIndex;
        }
        // Android : always use AAC
      } else if (userAgent.indexOf('android') !== -1) {
        adtsObjectType = 2;
        config = new Array(2);
        adtsExtensionSampleingIndex = adtsSampleingIndex;
      } else {
        /*  for other browsers (Chrome/Vivaldi/Opera ...)
            always force audio type to be HE-AAC SBR, as some browsers do not support audio codec switch properly (like Chrome ...)
        */
        adtsObjectType = 5;
        config = new Array(4);
        // if (manifest codec is HE-AAC or HE-AACv2) OR (manifest codec not specified AND frequency less than 24kHz)
        if ((audioCodec && ((audioCodec.indexOf('mp4a.40.29') !== -1) ||
          (audioCodec.indexOf('mp4a.40.5') !== -1))) ||
          (!audioCodec && adtsSampleingIndex >= 6)) {
          // HE-AAC uses SBR (Spectral Band Replication) , high frequencies are constructed from low frequencies
          // there is a factor 2 between frame sample rate and output sample rate
          // multiply frequency by 2 (see table below, equivalent to substract 3)
          adtsExtensionSampleingIndex = adtsSampleingIndex - 3;
        } else {
          // if (manifest codec is AAC) AND (frequency less than 24kHz AND nb channel is 1) OR (manifest codec not specified and mono audio)
          // Chrome fails to play back with low frequency AAC LC mono when initialized with HE-AAC.  This is not a problem with stereo.
          if (audioCodec && audioCodec.indexOf('mp4a.40.2') !== -1 && ((adtsSampleingIndex >= 6 && adtsChanelConfig === 1) ||
                /vivaldi/i.test(userAgent)) ||
            (!audioCodec && adtsChanelConfig === 1)) {
            adtsObjectType = 2;
            config = new Array(2);
          }
          adtsExtensionSampleingIndex = adtsSampleingIndex;
        }
      }
      /* refer to http://wiki.multimedia.cx/index.php?title=MPEG-4_Audio#Audio_Specific_Config
          ISO 14496-3 (AAC).pdf - Table 1.13 — Syntax of AudioSpecificConfig()
        Audio Profile / Audio Object Type
        0: Null
        1: AAC Main
        2: AAC LC (Low Complexity)
        3: AAC SSR (Scalable Sample Rate)
        4: AAC LTP (Long Term Prediction)
        5: SBR (Spectral Band Replication)
        6: AAC Scalable
       sampling freq
        0: 96000 Hz
        1: 88200 Hz
        2: 64000 Hz
        3: 48000 Hz
        4: 44100 Hz
        5: 32000 Hz
        6: 24000 Hz
        7: 22050 Hz
        8: 16000 Hz
        9: 12000 Hz
        10: 11025 Hz
        11: 8000 Hz
        12: 7350 Hz
        13: Reserved
        14: Reserved
        15: frequency is written explictly
        Channel Configurations
        These are the channel configurations:
        0: Defined in AOT Specifc Config
        1: 1 channel: front-center
        2: 2 channels: front-left, front-right
      */
      // audioObjectType = profile => profile, the MPEG-4 Audio Object Type minus 1
      config[0] = adtsObjectType << 3;
      // samplingFrequencyIndex
      config[0] |= (adtsSampleingIndex & 0x0E) >> 1;
      config[1] |= (adtsSampleingIndex & 0x01) << 7;
      // channelConfiguration
      config[1] |= adtsChanelConfig << 3;
      if (adtsObjectType === 5) {
        // adtsExtensionSampleingIndex
        config[1] |= (adtsExtensionSampleingIndex & 0x0E) >> 1;
        config[2] = (adtsExtensionSampleingIndex & 0x01) << 7;
        // adtsObjectType (force to 2, chrome is checking that object type is less than 5 ???
        //    https://chromium.googlesource.com/chromium/src.git/+/master/media/formats/mp4/aac.cc
        config[2] |= 2 << 2;
        config[3] = 0;
      }
      return { config: config, samplerate: adtsSampleingRates[adtsSampleingIndex], channelCount: adtsChanelConfig, codec: ('mp4a.40.' + adtsObjectType), manifestCodec: manifestCodec };
    }

    export function isHeaderPattern (data, offset) {
      return data[offset] === 0xff && (data[offset + 1] & 0xf6) === 0xf0;
    }

    export function getHeaderLength (data, offset) {
      return (data[offset + 1] & 0x01 ? 7 : 9);
    }

    export function getFullFrameLength (data, offset) {
      return ((data[offset + 3] & 0x03) << 11) |
        (data[offset + 4] << 3) |
        ((data[offset + 5] & 0xE0) >>> 5);
    }

    export function isHeader (data, offset) {
      // Look for ADTS header | 1111 1111 | 1111 X00X | where X can be either 0 or 1
      // Layer bits (position 14 and 15) in header should be always 0 for ADTS
      // More info https://wiki.multimedia.cx/index.php?title=ADTS
      if (offset + 1 < data.length && isHeaderPattern(data, offset)) {
        return true;
      }

      return false;
    }

    export function probe (data, offset) {
      // same as isHeader but we also check that ADTS frame follows last ADTS frame
      // or end of data is reached
      if (isHeader(data, offset)) {
        // ADTS header Length
        let headerLength = getHeaderLength(data, offset);
        // ADTS frame Length
        let frameLength = headerLength;
        if (offset + 5 < data.length) {
          frameLength = getFullFrameLength(data, offset);
        }

        let newOffset = offset + frameLength;
        if (newOffset === data.length || (newOffset + 1 < data.length && isHeaderPattern(data, newOffset))) {
          return true;
        }
      }
      return false;
    }

    export function initTrackConfig (track, observer, data, offset, audioCodec) {
      if (!track.samplerate) {
        let config = getAudioConfig(observer, data, offset, audioCodec);
        track.config = config.config;
        track.samplerate = config.samplerate;
        track.channelCount = config.channelCount;
        track.codec = config.codec;
        track.manifestCodec = config.manifestCodec;
        logger.log(`parsed codec:${track.codec},rate:${config.samplerate},nb channel:${config.channelCount}`);
      }
    }

    export function getFrameDuration (samplerate) {
      return 1024 * 90000 / samplerate;
    }

    export function parseFrameHeader (data, offset, pts, frameIndex, frameDuration) {
      let headerLength, frameLength, stamp;
      let length = data.length;

      // The protection skip bit tells us if we have 2 bytes of CRC data at the end of the ADTS header
      headerLength = getHeaderLength(data, offset);
      // retrieve frame size
      frameLength = getFullFrameLength(data, offset);
      frameLength -= headerLength;

      if ((frameLength > 0) && ((offset + headerLength + frameLength) <= length)) {
        stamp = pts + frameIndex * frameDuration;
        // logger.log(`AAC frame, offset/length/total/pts:${offset+headerLength}/${frameLength}/${data.byteLength}/${(stamp/90).toFixed(0)}`);
        return { headerLength, frameLength, stamp };
      }

      return undefined;
    }

    export function appendFrame (track, data, offset, pts, frameIndex) {
      let frameDuration = getFrameDuration(track.samplerate);
      let header = parseFrameHeader(data, offset, pts, frameIndex, frameDuration);
      if (header) {
        let stamp = header.stamp;
        let headerLength = header.headerLength;
        let frameLength = header.frameLength;

        // logger.log(`AAC frame, offset/length/total/pts:${offset+headerLength}/${frameLength}/${data.byteLength}/${(stamp/90).toFixed(0)}`);
        let aacSample = {
          unit: data.subarray(offset + headerLength, offset + headerLength + frameLength),
          pts: stamp,
          dts: stamp
        };

        track.samples.push(aacSample);
        return { sample: aacSample, length: frameLength + headerLength };
      }

      return undefined;
    }