static double lengthOfWAVInSeconds(File wavFile) {
  if (!fileExists(wavFile)) ret 0;
  temp WAVDecoder decoder = new(fileInputStream(wavFile));
  short[] s = new short[1];
  int n = 0;
  while (decoder.readMonoSamples(s) != 0) ++n;
  ret n/decoder.sampleRate;
}