sclass AudioInputStreamsCollector {
  new L<InputStream> streams;
  int frames;
  
  void add(InputStream stream, int frames) {
    streams.add(stream);
    this.frames += frames;
  }
  
  void addSilence(double seconds) {
    int n = iround(seconds/2);
    add(ZerosInputStream(n*2), n);
  }
}