computePeaks static method

Float32List computePeaks(Uint8List pcm, int sampleRate)

Max absolute amplitude per bucket of 16-bit mono pcm, normalized to the loudest bucket.

Implementation

static Float32List computePeaks(Uint8List pcm, int sampleRate) {
  final data = ByteData.sublistView(pcm);
  final samples = pcm.length ~/ 2;
  final bucket = math.max(1, sampleRate ~/ peaksPerSecond);
  final count = (samples / bucket).ceil();
  final peaks = Float32List(count);
  var loudest = 1;
  for (var b = 0; b < count; b++) {
    var peak = 0;
    final end = math.min(samples, (b + 1) * bucket);
    for (var i = b * bucket; i < end; i++) {
      final v = data.getInt16(i * 2, Endian.little).abs();
      if (v > peak) peak = v;
    }
    peaks[b] = peak.toDouble();
    if (peak > loudest) loudest = peak;
  }
  for (var b = 0; b < count; b++) {
    peaks[b] = peaks[b] / loudest;
  }
  return peaks;
}