getAmplitudes method

@override Future<List<int>> getAmplitudes(String filePath, int samplesPerSecond)

Implementation

@override
Future<List<int>> getAmplitudes(String filePath, int samplesPerSecond) async {
  if (samplesPerSecond <= 0) {
    throw ArgumentError.value(
      samplesPerSecond,
      'samplesPerSecond',
      'must be greater than 0',
    );
  }

  final web.Response response = await web.window.fetch(filePath.toJS).toDart;
  if (!response.ok) {
    throw Exception(
      'Failed to fetch "$filePath" (HTTP ${response.status}).',
    );
  }
  final JSArrayBuffer encoded = await response.arrayBuffer().toDart;

  final web.AudioContext context = web.AudioContext();
  try {
    final web.AudioBuffer decoded =
        await context.decodeAudioData(encoded).toDart;
    final Float32List channelData = decoded.getChannelData(0).toDart;
    final int windowSize =
        math.max(1, (decoded.sampleRate / samplesPerSecond).floor());
    final List<int> amplitudes = <int>[];

    for (int i = 0; i < channelData.length; i += windowSize) {
      final int end = math.min(i + windowSize, channelData.length);
      double sumSquares = 0;
      for (int j = i; j < end; j++) {
        final double sample = channelData[j].toDouble();
        sumSquares += sample * sample;
      }

      final double rms = math.sqrt(sumSquares / (end - i));
      final int normalized = (rms * 100).round().clamp(0, 100);
      amplitudes.add(normalized);
    }

    return amplitudes;
  } finally {
    await context.close().toDart;
  }
}