code: public int addSoundtrack(OggAudioHeaders audio) {
          if (w == null) {
              throw new IllegalStateException("Not in write mode");
          }
  
          // If it doesn't have a sid yet, get it one
          OggPacketWriter aw = null;
          if (audio.getSid() == -1) {
              aw = ogg.getPacketWriter();
              // TODO How to tell the OggAudioHeaders the new SID?
          } else {
              aw = ogg.getPacketWriter(audio.getSid());
          }
          int audioSid = aw.getSid();
  
          // If we have a skeleton, tell it about the new stream
          if (skeleton != null) {
              SkeletonFisbone bone = skeleton.addBoneForStream(audioSid);
              bone.setContentType(audio.getType().mimetype);
              // TODO Populate the rest of the bone as best we can
          }
  
          // Record the new audio stream
          soundtracks.put(audioSid, (OggAudioStreamHeaders)audio);
          soundtrackWriters.put((OggAudioStreamHeaders)audio, aw);
  
          // Report the sid
          return audioSid;
      }
docs: Adds a new soundtrack to the video
  
  @return the serial id (sid) of the new soundtrack