code: public void writeAudioData(OggStreamAudioData data, int audioSid) {
          if (! soundtracks.containsKey(audioSid)) {
              throw new IllegalArgumentException("Unknown audio stream with id " + audioSid);
          }
  
          writtenPackets.add(new AudioVisualDataAndSid(data, audioSid));
      }
docs: Buffers the given audio ready for writing
  out, to a given (pre-existing) audio stream.
  Data won't be written out yet, you
  need to call {@link #close()} to do that,
  because we assume you'll still be populating
  the Info/Comment/Setup objects