mux.js

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We have HLS source where ts segments contain one VIDEO, multiple AUDIO tracks in a segment file. Current mux.ts library takes any first audio PID even if it was an additional type=visual_impaired track.

We cannot control the ordering of audio or remuxing to separate m3u8 manifest tracks. I made changes to parsePmt function to select first normal_audio and fallback to any first audio (current behaviour) if normal audio was not found.

I think this would be usefull be a default in muxjs library? This simple rule works fine even if audio PIDs or language codes changed while playing a hls ts stream, transition from one programme to next one may have different audio component tags, but no problem.

      parsePmt = function parsePmt(payload, pmt) {
        var sectionLength, tableEnd, programInfoLength, offset; // PMTs can be sent ahead of the time when they should actually
        // take effect. We don't believe this should ever be the case
        // for HLS but we'll ignore "forward" PMT declarations if we see
        // them. Future PMT declarations have the current_next_indicator
        // set to zero.

        if (!(payload[5] & 0x01)) {
          return;
        } // overwrite any existing program map table

        var firstAudio=null, firstAudioNormal=null;
        self.programMapTable = {
          video: null,
          audio: null,
          'timed-metadata': {}
        }; // the mapping table ends at the end of the current section

        sectionLength = (payload[1] & 0x0f) << 8 | payload[2];
        tableEnd = 3 + sectionLength - 4; // to determine where the table is, we have to figure out how
        // long the program info descriptors are

        programInfoLength = (payload[10] & 0x0f) << 8 | payload[11]; // advance the offset to the first entry in the mapping table
        offset = 12 + programInfoLength;

        while (offset < tableEnd) {
          // 27=VIDEO_h264, 15=AUDIO_adtsaac, 6=SUBTITLE_dvb
          var streamType = payload[offset];
          var pid = (payload[offset + 1] & 0x1F) << 8 | payload[offset + 2]; // only map a single elementary_pid for audio and video stream types
          // TODO: should this be done for metadata too? for now maintain behavior of multiple metadata streams

          // parse audio components, skip visualimpaired audio and take any first normal audio
          var infoLen = ((payload[offset + 3] & 0x0F) << 8 | payload[offset + 4]);
          var descLang="";
          var descType=0xFF; //0x00=normal_audio, 0x03=visual_impaired_audio
          if(payload[offset+5]==0x0A || payload[offset+5]==0x59) { // 0x0A=langDesc, 0x59=subDesc
            var descLen = payload[offset+6];
            if(descLen>=4) {
              descLang= String.fromCharCode(payload[offset+7]) 
                + String.fromCharCode(payload[offset+8])
                + String.fromCharCode(payload[offset+9]);
              descType=payload[offset+10]
            }
          }
         // console.log(`type=${streamType}, pid=${pid}` +"(0x"+bin.toHexString(pid)+"), infoLen="+infoLen 
         //    + ", lang="+descLang + ", type="+ descType);

          if (streamType === streamTypes.H264_STREAM_TYPE && self.programMapTable.video === null) {
            self.programMapTable.video = pid;
          //} else if (streamType === streamTypes.ADTS_STREAM_TYPE && self.programMapTable.audio === null) {
            //self.programMapTable.audio = pid;			
          } else if (streamType === streamTypes.ADTS_STREAM_TYPE) {
            if(firstAudio===null) firstAudio=pid; // any first audio even visual_impaired_audio
            if(firstAudioNormal===null && descType==0x00) firstAudioNormal=pid; // first normal_audio
          } else if (streamType === streamTypes.METADATA_STREAM_TYPE) {
            // map pid to stream type for metadata streams
            self.programMapTable['timed-metadata'][pid] = streamType;
          } // move to the next table entry
          // skip past the elementary stream descriptors, if present
          
          offset += infoLen+5; //offset += ((payload[offset + 3] & 0x0F) << 8 | payload[offset + 4]) + 5;
        } // record the map on the packet as well

        self.programMapTable.audio = firstAudioNormal!=null ? firstAudioNormal : firstAudio;
        pmt.programMapTable = self.programMapTable;
      };

Or how do videojs|muxjs works any ideas how to inject an application callback to parsePmt function? Something like track = appCallback.selectAudioTrack(tracks[ list of streamType, descLang, descType, pid ]) let application decide a priority logic?