static VF1<double[]> stereoSamplesIterator_single(final short[] samples, final Runnable whenDone) {
  ret new VF1<double[]>() {
    int sampleIndex = 0;
    public void get(double[] pair) {
      if (sampleIndex >= l(samples))
        ret with pair[0] = Double.NaN;
      pair[0] = samples[sampleIndex];
      pair[1] = samples[sampleIndex+1];
      sampleIndex += 2;
      if (sampleIndex >= l(samples))
        callF(whenDone);
    }
  };
}