just_waveform 0.0.2

Extracts waveform data from an audio file suitable for visually rendering the waveform.

example/lib/main.dart

import 'dart:io';
import 'dart:math';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';
import 'package:rxdart/rxdart.dart';
import 'package:just_waveform/just_waveform.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final progressStream = BehaviorSubject<WaveformProgress>();

  @override
  void initState() {
    super.initState();
    _init();
  }

  Future<void> _init() async {
    final audioFile =
        File(p.join((await getTemporaryDirectory()).path, 'waveform.mp3'));
    try {
      await audioFile.writeAsBytes(
          (await rootBundle.load('audio/waveform.mp3')).buffer.asUint8List());
      final waveFile =
          File(p.join((await getTemporaryDirectory()).path, 'waveform.wave'));
      JustWaveform.extract(audioInFile: audioFile, waveOutFile: waveFile)
          .listen(progressStream.add, onError: progressStream.addError);
    } catch (e) {
      progressStream.addError(e);
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Plugin example app'),
        ),
        body: Container(
          alignment: Alignment.center,
          padding: const EdgeInsets.all(16.0),
          child: Container(
            height: 150.0,
            decoration: BoxDecoration(
              color: Colors.grey.shade200,
              borderRadius: const BorderRadius.all(Radius.circular(20.0)),
            ),
            padding: const EdgeInsets.all(16.0),
            width: double.maxFinite,
            child: StreamBuilder<WaveformProgress>(
              stream: progressStream,
              builder: (context, snapshot) {
                if (snapshot.hasError) {
                  return Center(
                    child: Text(
                      'Error: ${snapshot.error}',
                      style: Theme.of(context).textTheme.headline6,
                      textAlign: TextAlign.center,
                    ),
                  );
                }
                final progress = snapshot.data?.progress ?? 0.0;
                final waveform = snapshot.data?.waveform;
                if (waveform == null) {
                  return Center(
                    child: Text(
                      '${(100 * progress).toInt()}%',
                      style: Theme.of(context).textTheme.headline6,
                    ),
                  );
                }
                return AudioWaveformWidget(
                  waveform: waveform,
                  start: Duration.zero,
                  duration: waveform.duration,
                );
              },
            ),
          ),
        ),
      ),
    );
  }
}

class AudioWaveformWidget extends StatefulWidget {
  final Color waveColor;
  final double scale;
  final double strokeWidth;
  final double pixelsPerStep;
  final Waveform waveform;
  final Duration start;
  final Duration duration;

  const AudioWaveformWidget({
    Key? key,
    required this.waveform,
    required this.start,
    required this.duration,
    this.waveColor = Colors.blue,
    this.scale = 1.0,
    this.strokeWidth = 5.0,
    this.pixelsPerStep = 8.0,
  }) : super(key: key);

  @override
  _AudioWaveformState createState() => _AudioWaveformState();
}

class _AudioWaveformState extends State<AudioWaveformWidget> {
  @override
  Widget build(BuildContext context) {
    return ClipRect(
      child: CustomPaint(
        painter: AudioWaveformPainter(
          waveColor: widget.waveColor,
          waveform: widget.waveform,
          start: widget.start,
          duration: widget.duration,
          scale: widget.scale,
          strokeWidth: widget.strokeWidth,
          pixelsPerStep: widget.pixelsPerStep,
        ),
      ),
    );
  }
}

class AudioWaveformPainter extends CustomPainter {
  final double scale;
  final double strokeWidth;
  final double pixelsPerStep;
  final Paint wavePaint;
  final Waveform waveform;
  final Duration start;
  final Duration duration;

  AudioWaveformPainter({
    required this.waveform,
    required this.start,
    required this.duration,
    Color waveColor = Colors.blue,
    this.scale = 1.0,
    this.strokeWidth = 5.0,
    this.pixelsPerStep = 8.0,
  }) : wavePaint = Paint()
          ..style = PaintingStyle.stroke
          ..strokeWidth = strokeWidth
          ..strokeCap = StrokeCap.round
          ..color = waveColor;

  @override
  void paint(Canvas canvas, Size size) {
    if (duration == Duration.zero) return;

    double width = size.width;
    double height = size.height;

    final waveformPixelsPerWindow = waveform.positionToPixel(duration).toInt();
    final waveformPixelsPerDevicePixel = waveformPixelsPerWindow / width;
    final waveformPixelsPerStep = waveformPixelsPerDevicePixel * pixelsPerStep;
    final sampleOffset = waveform.positionToPixel(start);
    final sampleStart = -sampleOffset % waveformPixelsPerStep;
    for (var i = sampleStart.toDouble();
        i <= waveformPixelsPerWindow + 1.0;
        i += waveformPixelsPerStep) {
      final sampleIdx = (sampleOffset + i).toInt();
      final x = i / waveformPixelsPerDevicePixel;
      final minY = normalise(waveform.getPixelMin(sampleIdx), height);
      final maxY = normalise(waveform.getPixelMax(sampleIdx), height);
      canvas.drawLine(
        Offset(x + strokeWidth / 2, max(strokeWidth * 0.75, minY)),
        Offset(x + strokeWidth / 2, min(height - strokeWidth * 0.75, maxY)),
        wavePaint,
      );
    }
  }

  @override
  bool shouldRepaint(covariant AudioWaveformPainter oldDelegate) {
    return false;
  }

  double normalise(int s, double height) {
    if (waveform.flags == 0) {
      final y = 32768 + (scale * s).clamp(-32768.0, 32767.0).toDouble();
      return height - 1 - y * height / 65536;
    } else {
      final y = 128 + (scale * s).clamp(-128.0, 127.0).toDouble();
      return height - 1 - y * height / 256;
    }
  }
}