flutter_gapless_loop 0.0.2 
flutter_gapless_loop: ^0.0.2 copied to clipboard
True sample-accurate gapless audio looping on iOS (AVAudioEngine) and Android (AudioTrack). Zero-gap, zero-click loop playback for music production apps.
example/lib/main.dart
import 'dart:async';
import 'dart:math' as math;
import 'dart:typed_data';
import 'package:flutter/material.dart';
import 'package:file_picker/file_picker.dart';
import 'package:flutter_gapless_loop/flutter_gapless_loop.dart';
void main() {
runApp(const GaplessLoopApp());
}
class GaplessLoopApp extends StatelessWidget {
const GaplessLoopApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Gapless Loop Demo',
theme: ThemeData(
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
useMaterial3: true,
),
home: const GaplessLoopScreen(),
);
}
}
class GaplessLoopScreen extends StatefulWidget {
const GaplessLoopScreen({super.key});
@override
State<GaplessLoopScreen> createState() => _GaplessLoopScreenState();
}
class _GaplessLoopScreenState extends State<GaplessLoopScreen> {
final _player = LoopAudioPlayer();
PlayerState _state = PlayerState.idle;
double _duration = 0.0;
double _position = 0.0;
double _loopStart = 0.0;
double _loopEnd = 0.0;
double _crossfade = 0.0; // 0 to 0.5 seconds
double _volume = 1.0;
double _pan = 0.0;
// BPM controls
double _detectedBpm = 0.0; // auto-detected; used as rate base
double _manualBpm = 0.0;
final _bpmController = TextEditingController();
final List<DateTime> _tapTimes = [];
Timer? _bpmRepeatTimer;
bool _longPressActive = false;
BpmResult? _bpmResult;
StreamSubscription<PlayerState>? _stateSub;
StreamSubscription<String>? _errorSub;
StreamSubscription<BpmResult>? _bpmSub;
Timer? _positionTimer;
@override
void initState() {
super.initState();
_stateSub = _player.stateStream.listen(_onStateChange);
_errorSub = _player.errorStream.listen(_onError);
_bpmSub = _player.bpmStream.listen((r) {
setState(() {
_bpmResult = r;
if (r.bpm > 0) {
_detectedBpm = r.bpm;
_manualBpm = r.bpm;
_bpmController.text = r.bpm.toStringAsFixed(1);
}
});
// Rate is 1.0 when manualBpm == detectedBpm, so nothing changes on detection.
});
}
@override
void dispose() {
_stateSub?.cancel();
_errorSub?.cancel();
_bpmSub?.cancel();
_positionTimer?.cancel();
_bpmRepeatTimer?.cancel();
_bpmController.dispose();
_player.dispose();
super.dispose();
}
void _onStateChange(PlayerState state) {
setState(() => _state = state);
if (state == PlayerState.playing) {
_startPositionTimer();
} else {
_stopPositionTimer();
}
}
void _onError(String message) {
if (!mounted) return;
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(content: Text('Error: $message'), backgroundColor: Colors.red),
);
}
void _startPositionTimer() {
_positionTimer?.cancel();
_positionTimer = Timer.periodic(const Duration(milliseconds: 200), (_) async {
if (!mounted) return;
final pos = await _player.currentPosition;
setState(() => _position = pos);
});
}
void _stopPositionTimer() {
_positionTimer?.cancel();
_positionTimer = null;
}
Future<void> _pickFile() async {
final result = await FilePicker.platform.pickFiles(
type: FileType.custom,
allowedExtensions: ['wav', 'aiff', 'aif', 'mp3', 'm4a'],
);
if (result == null || result.files.single.path == null) return;
final path = result.files.single.path!;
try {
await _player.loadFromFile(path);
final dur = await _player.duration;
_tapTimes.clear();
await _player.setPlaybackRate(1.0);
setState(() {
_duration = dur.inMilliseconds / 1000.0;
_loopStart = 0.0;
_loopEnd = _duration;
_position = 0.0;
_bpmResult = null; // cleared until bpmStream fires
_detectedBpm = 0.0;
_manualBpm = 0.0;
_bpmController.text = '';
});
} catch (e) {
_onError(e.toString());
}
}
Future<void> _play() async {
try {
await _player.play();
} catch (e) {
_onError(e.toString());
}
}
Future<void> _pause() async {
try {
await _player.pause();
} catch (e) {
_onError(e.toString());
}
}
Future<void> _stop() async {
try {
await _player.stop();
setState(() => _position = 0.0);
} catch (e) {
_onError(e.toString());
}
}
Future<void> _setLoopRegion() async {
if (_loopEnd <= _loopStart) return;
try {
await _player.setLoopRegion(_loopStart, _loopEnd);
} catch (e) {
_onError(e.toString());
}
}
Future<void> _setCrossfade(double value) async {
setState(() => _crossfade = value);
try {
await _player.setCrossfadeDuration(value);
} catch (e) {
_onError(e.toString());
}
}
Future<void> _setVolume(double value) async {
setState(() => _volume = value);
try {
await _player.setVolume(value);
} catch (e) {
_onError(e.toString());
}
}
void _applyPlaybackRate() {
if (_detectedBpm <= 0 || !_isReady) return;
final rate = _manualBpm / _detectedBpm;
_player.setPlaybackRate(rate).catchError((_) {});
}
void _adjustBpm(double delta) {
setState(() {
_manualBpm = (_manualBpm + delta).clamp(20.0, 300.0).toDouble();
_bpmController.text = _manualBpm.toStringAsFixed(1);
});
_applyPlaybackRate();
}
void _onTapTempo() {
final now = DateTime.now();
if (_tapTimes.isNotEmpty &&
now.difference(_tapTimes.last).inMilliseconds > 3000) {
_tapTimes.clear();
}
_tapTimes.add(now);
if (_tapTimes.length > 8) _tapTimes.removeAt(0);
if (_tapTimes.length >= 2) {
final intervals = <double>[];
for (int i = 1; i < _tapTimes.length; i++) {
intervals.add(
_tapTimes[i].difference(_tapTimes[i - 1]).inMilliseconds / 1000.0);
}
final avg = intervals.reduce((a, b) => a + b) / intervals.length;
setState(() {
_manualBpm = (60.0 / avg).clamp(20.0, 300.0).toDouble();
_bpmController.text = _manualBpm.toStringAsFixed(1);
});
_applyPlaybackRate();
}
}
void _snapToBeat() {
if (_manualBpm <= 0 || !_isReady) return;
final beatPeriod = 60.0 / _manualBpm;
var newStart = (_loopStart / beatPeriod).round() * beatPeriod;
var newEnd = (_loopEnd / beatPeriod).round() * beatPeriod;
newStart = newStart.clamp(0.0, _duration);
newEnd = newEnd.clamp(0.0, _duration);
if (newStart >= newEnd) return;
setState(() {
_loopStart = newStart;
_loopEnd = newEnd;
});
_setLoopRegion();
}
Future<void> _setPan(double value) async {
setState(() => _pan = value);
try {
await _player.setPan(value);
} catch (e) {
_onError(e.toString());
}
}
bool get _isReady =>
_state != PlayerState.idle && _state != PlayerState.loading;
String get _stateLabel {
switch (_state) {
case PlayerState.idle: return 'Idle — pick a file to begin';
case PlayerState.loading: return 'Loading...';
case PlayerState.ready: return 'Ready';
case PlayerState.playing: return 'Playing';
case PlayerState.paused: return 'Paused';
case PlayerState.stopped: return 'Stopped';
case PlayerState.error: return 'Error';
}
}
String _fmt(double secs) => secs.toStringAsFixed(2);
@override
Widget build(BuildContext context) {
final progress = _duration > 0 ? (_position / _duration).clamp(0.0, 1.0) : 0.0;
return Scaffold(
appBar: AppBar(
title: const Text('Gapless Loop Demo'),
backgroundColor: Theme.of(context).colorScheme.inversePrimary,
),
body: SingleChildScrollView(
padding: const EdgeInsets.all(16),
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
// ── File picker + state label ──────────────────────────
Row(
children: [
ElevatedButton.icon(
onPressed: _pickFile,
icon: const Icon(Icons.folder_open),
label: const Text('Pick Audio File'),
),
const SizedBox(width: 16),
Expanded(
child: Text(
_stateLabel,
style: Theme.of(context).textTheme.bodyMedium,
overflow: TextOverflow.ellipsis,
),
),
],
),
const SizedBox(height: 16),
// ── Progress bar ───────────────────────────────────────
Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
LinearProgressIndicator(value: progress, minHeight: 8),
const SizedBox(height: 4),
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
Text(_fmt(_position), style: Theme.of(context).textTheme.bodySmall),
Text(_fmt(_duration), style: Theme.of(context).textTheme.bodySmall),
],
),
],
),
const SizedBox(height: 16),
// ── Transport controls ─────────────────────────────────
Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
ElevatedButton.icon(
onPressed: _isReady && _state != PlayerState.playing ? _play : null,
icon: const Icon(Icons.play_arrow),
label: const Text('Play'),
),
ElevatedButton.icon(
onPressed: _isReady && _state == PlayerState.playing ? _pause : null,
icon: const Icon(Icons.pause),
label: const Text('Pause'),
),
ElevatedButton.icon(
onPressed: _isReady ? _stop : null,
icon: const Icon(Icons.stop),
label: const Text('Stop'),
),
],
),
const SizedBox(height: 24),
const Divider(),
// ── Loop region ────────────────────────────────────────
Text('Loop Region', style: Theme.of(context).textTheme.titleSmall),
const SizedBox(height: 8),
Row(
children: [
SizedBox(
width: 90,
child: Text('Start: ${_fmt(_loopStart)}s',
style: Theme.of(context).textTheme.bodySmall),
),
Expanded(
child: Slider(
value: _loopStart.clamp(0.0, _duration > 0 ? _duration : 1.0),
min: 0.0,
max: _duration > 0 ? _duration : 1.0,
divisions: _duration > 0 ? (_duration * 10).toInt().clamp(1, 1000) : 1,
onChanged: _isReady
? (v) {
setState(() => _loopStart = v);
}
: null,
onChangeEnd: _isReady ? (_) => _setLoopRegion() : null,
),
),
],
),
Row(
children: [
SizedBox(
width: 90,
child: Text('End: ${_fmt(_loopEnd)}s',
style: Theme.of(context).textTheme.bodySmall),
),
Expanded(
child: Slider(
value: _loopEnd.clamp(0.0, _duration > 0 ? _duration : 1.0),
min: 0.0,
max: _duration > 0 ? _duration : 1.0,
divisions: _duration > 0 ? (_duration * 10).toInt().clamp(1, 1000) : 1,
onChanged: _isReady
? (v) {
setState(() => _loopEnd = v);
}
: null,
onChangeEnd: _isReady ? (_) => _setLoopRegion() : null,
),
),
],
),
const Divider(),
// ── Crossfade ──────────────────────────────────────────
Text('Crossfade', style: Theme.of(context).textTheme.titleSmall),
Row(
children: [
SizedBox(
width: 90,
child: Text('${(_crossfade * 1000).toStringAsFixed(0)}ms',
style: Theme.of(context).textTheme.bodySmall),
),
Expanded(
child: Slider(
value: _crossfade,
min: 0.0,
max: 0.5,
divisions: 50,
onChanged: _isReady ? _setCrossfade : null,
),
),
],
),
const Divider(),
// ── Volume ─────────────────────────────────────────────
Text('Volume', style: Theme.of(context).textTheme.titleSmall),
Row(
children: [
SizedBox(
width: 90,
child: Text(_volume.toStringAsFixed(2),
style: Theme.of(context).textTheme.bodySmall),
),
Expanded(
child: Slider(
value: _volume,
min: 0.0,
max: 1.0,
divisions: 100,
onChanged: _isReady ? _setVolume : null,
),
),
],
),
const Divider(),
// ── BPM Detection ──────────────────────────────────────
Text('BPM Detection', style: Theme.of(context).textTheme.titleSmall),
const SizedBox(height: 8),
_BpmCard(result: _bpmResult, isReady: _isReady),
const Divider(),
// ── BPM Controls ──────────────────────────────────────────
Text('BPM Controls', style: Theme.of(context).textTheme.titleSmall),
const SizedBox(height: 8),
Row(
children: [
// Decrement button with long-press repeat
GestureDetector(
onLongPressStart: (_) {
_longPressActive = true;
_bpmRepeatTimer = Timer(const Duration(milliseconds: 400), () {
if (!_longPressActive) return;
_bpmRepeatTimer = Timer.periodic(
const Duration(milliseconds: 100), (_) => _adjustBpm(-1.0));
});
},
onLongPressEnd: (_) {
_longPressActive = false;
_bpmRepeatTimer?.cancel();
_bpmRepeatTimer = null;
},
child: IconButton(
icon: const Icon(Icons.remove),
onPressed: _isReady ? () => _adjustBpm(-1.0) : null,
),
),
// Manual BPM text field
Expanded(
child: TextField(
controller: _bpmController,
keyboardType: const TextInputType.numberWithOptions(decimal: true),
decoration: const InputDecoration(
labelText: 'BPM',
isDense: true,
border: OutlineInputBorder(),
),
enabled: _isReady,
onSubmitted: (v) {
final parsed = double.tryParse(v);
if (parsed != null) {
setState(() {
_manualBpm = parsed.clamp(20.0, 300.0).toDouble();
_bpmController.text = _manualBpm.toStringAsFixed(1);
});
_applyPlaybackRate();
} else {
_bpmController.text = _manualBpm > 0 ? _manualBpm.toStringAsFixed(1) : '';
}
},
),
),
// Increment button with long-press repeat
GestureDetector(
onLongPressStart: (_) {
_longPressActive = true;
_bpmRepeatTimer = Timer(const Duration(milliseconds: 400), () {
if (!_longPressActive) return;
_bpmRepeatTimer = Timer.periodic(
const Duration(milliseconds: 100), (_) => _adjustBpm(1.0));
});
},
onLongPressEnd: (_) {
_longPressActive = false;
_bpmRepeatTimer?.cancel();
_bpmRepeatTimer = null;
},
child: IconButton(
icon: const Icon(Icons.add),
onPressed: _isReady ? () => _adjustBpm(1.0) : null,
),
),
],
),
const SizedBox(height: 8),
Row(
children: [
ElevatedButton.icon(
onPressed: _isReady ? _onTapTempo : null,
icon: const Icon(Icons.touch_app),
label: const Text('Tap Tempo'),
),
const SizedBox(width: 8),
ElevatedButton.icon(
onPressed: _isReady && _manualBpm > 0 ? _snapToBeat : null,
icon: const Icon(Icons.grid_on),
label: const Text('Snap to Beat'),
),
],
),
if (_detectedBpm > 0 && _manualBpm > 0)
Padding(
padding: const EdgeInsets.only(top: 4),
child: Text(
'Speed: ×${(_manualBpm / _detectedBpm).toStringAsFixed(2)}',
style: Theme.of(context).textTheme.bodySmall?.copyWith(
color: Theme.of(context).colorScheme.primary,
),
),
),
const Divider(),
// ── Panning ────────────────────────────────────────────────
Text('Panning', style: Theme.of(context).textTheme.titleSmall),
Row(
children: [
const SizedBox(width: 24, child: Text('L', textAlign: TextAlign.center)),
Expanded(
child: Slider(
value: _pan,
min: -1.0,
max: 1.0,
divisions: 200,
onChanged: _isReady ? _setPan : null,
),
),
const SizedBox(width: 24, child: Text('R', textAlign: TextAlign.center)),
],
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
_pan == 0.0
? 'Centre'
: _pan < 0
? 'L ${(-_pan * 100).toStringAsFixed(0)}%'
: 'R ${(_pan * 100).toStringAsFixed(0)}%',
style: Theme.of(context).textTheme.bodySmall,
),
],
),
const Divider(),
// ── Metronome ──────────────────────────────────────────────
const _MetronomeCard(),
],
),
),
);
}
}
/// Generates a short sine-burst as a raw WAV [Uint8List].
///
/// [freq] — frequency in Hz (e.g. 880 for click, 1760 for accent).
/// [durationMs] — length in milliseconds.
/// [amplitude] — peak amplitude 0.0–1.0.
Uint8List _generateSineWav({
required double freq,
required int durationMs,
double amplitude = 0.8,
int sampleRate = 44100,
}) {
final numSamples = (sampleRate * durationMs / 1000).round();
final pcm = Int16List(numSamples);
for (var i = 0; i < numSamples; i++) {
final t = i / sampleRate;
// 5 ms fade-in, 20 ms fade-out to prevent clicks
double env = 1.0;
final fadeInFrames = (sampleRate * 0.005).round();
final fadeOutFrames = (sampleRate * 0.020).round();
if (i < fadeInFrames) {
env = i / fadeInFrames;
} else if (i > numSamples - fadeOutFrames) {
env = (numSamples - i) / fadeOutFrames;
}
pcm[i] = (amplitude * env * 32767 * math.sin(2 * math.pi * freq * t))
.round()
.clamp(-32768, 32767);
}
final dataBytes = pcm.buffer.asUint8List();
final totalBytes = 44 + dataBytes.length;
final header = ByteData(44)
..setUint32(0, 0x52494646, Endian.big) // "RIFF"
..setUint32(4, totalBytes - 8, Endian.little)
..setUint32(8, 0x57415645, Endian.big) // "WAVE"
..setUint32(12, 0x666d7420, Endian.big) // "fmt "
..setUint32(16, 16, Endian.little) // chunk size
..setUint16(20, 1, Endian.little) // PCM
..setUint16(22, 1, Endian.little) // mono
..setUint32(24, sampleRate, Endian.little)
..setUint32(28, sampleRate * 2, Endian.little) // byte rate
..setUint16(32, 2, Endian.little) // block align
..setUint16(34, 16, Endian.little) // bits per sample
..setUint32(36, 0x64617461, Endian.big) // "data"
..setUint32(40, dataBytes.length, Endian.little);
return Uint8List.fromList([...header.buffer.asUint8List(), ...dataBytes]);
}
// ──────────────────────────────────────────────────────────────────────────────
// Metronome Card
// ──────────────────────────────────────────────────────────────────────────────
class _MetronomeCard extends StatefulWidget {
const _MetronomeCard();
@override
State<_MetronomeCard> createState() => _MetronomeCardState();
}
class _MetronomeCardState extends State<_MetronomeCard> {
final _metronome = MetronomePlayer();
bool _running = false;
double _bpm = 100.0;
int _beatsPerBar = 4;
int _currentBeat = -1;
StreamSubscription<int>? _beatSub;
// Pre-generate click and accent WAV bytes once (static, reused across rebuilds).
static final _clickBytes = _generateSineWav(freq: 880, durationMs: 40);
static final _accentBytes = _generateSineWav(freq: 1760, durationMs: 50, amplitude: 1.0);
@override
void dispose() {
_beatSub?.cancel();
_metronome.dispose();
super.dispose();
}
Future<void> _toggleMetronome() async {
if (_running) {
await _metronome.stop();
_beatSub?.cancel();
setState(() { _running = false; _currentBeat = -1; });
} else {
await _metronome.start(
bpm: _bpm,
beatsPerBar: _beatsPerBar,
click: _clickBytes,
accent: _accentBytes,
);
_beatSub = _metronome.beatStream.listen((beat) {
if (mounted) setState(() => _currentBeat = beat);
});
setState(() => _running = true);
}
}
@override
Widget build(BuildContext context) {
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text('Metronome', style: Theme.of(context).textTheme.titleSmall),
const SizedBox(height: 12),
// ── Beat indicator dots ────────────────────────────────
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: List.generate(_beatsPerBar, (i) {
final isActive = _running && i == _currentBeat;
return AnimatedContainer(
duration: const Duration(milliseconds: 80),
margin: const EdgeInsets.symmetric(horizontal: 6),
width: 28, height: 28,
decoration: BoxDecoration(
shape: BoxShape.circle,
color: isActive
? (i == 0 ? Colors.orange : Colors.blue)
: Colors.grey.shade300,
),
);
}),
),
const SizedBox(height: 16),
// ── BPM slider ─────────────────────────────────────────
Row(
children: [
const SizedBox(width: 50, child: Text('BPM')),
Expanded(
child: Slider(
value: _bpm,
min: 40, max: 240,
divisions: 200,
label: _bpm.round().toString(),
onChanged: (v) async {
setState(() => _bpm = v);
if (_running) await _metronome.setBpm(v);
},
),
),
SizedBox(width: 36, child: Text(_bpm.round().toString())),
],
),
// ── Time signature ─────────────────────────────────────
Row(
children: [
const SizedBox(width: 50, child: Text('Time')),
DropdownButton<int>(
value: _beatsPerBar,
items: [2, 3, 4, 5, 6, 7]
.map((n) => DropdownMenuItem(value: n, child: Text('$n/4')))
.toList(),
onChanged: (v) async {
if (v == null) return;
setState(() { _beatsPerBar = v; _currentBeat = -1; });
if (_running) await _metronome.setBeatsPerBar(v);
},
),
],
),
const SizedBox(height: 12),
// ── Start / Stop button ────────────────────────────────
Center(
child: ElevatedButton.icon(
onPressed: _toggleMetronome,
icon: Icon(_running ? Icons.stop : Icons.play_arrow),
label: Text(_running ? 'Stop' : 'Start'),
style: ElevatedButton.styleFrom(
backgroundColor: _running ? Colors.red : Colors.green,
foregroundColor: Colors.white,
),
),
),
],
);
}
}
// ──────────────────────────────────────────────────────────────────────────────
class _BpmCard extends StatelessWidget {
const _BpmCard({required this.result, required this.isReady});
final BpmResult? result;
final bool isReady;
@override
Widget build(BuildContext context) {
if (!isReady) {
return const Text('Load a file to see BPM detection results.',
style: TextStyle(color: Colors.grey));
}
if (result == null) {
return const Row(
children: [
SizedBox(width: 16, height: 16, child: CircularProgressIndicator(strokeWidth: 2)),
SizedBox(width: 8),
Text('Detecting BPM...'),
],
);
}
final r = result!;
if (r.bpm == 0.0) {
return const Text('No BPM detected (audio too short or silent).',
style: TextStyle(color: Colors.grey));
}
final confidencePct = (r.confidence * 100).toStringAsFixed(0);
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
'${r.bpm.toStringAsFixed(1)} BPM',
style: Theme.of(context).textTheme.headlineMedium?.copyWith(
fontWeight: FontWeight.bold,
color: Theme.of(context).colorScheme.primary,
),
),
const SizedBox(height: 4),
Text('Confidence: $confidencePct% · ${r.beats.length} beats detected',
style: Theme.of(context).textTheme.bodySmall),
if (r.beatsPerBar > 0) ...[
const SizedBox(height: 2),
Text(
'${r.beatsPerBar}/4 time · ${r.bars.length} bars',
style: Theme.of(context).textTheme.bodySmall,
),
],
],
);
}
}Metadata
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Metadata
True sample-accurate gapless audio looping on iOS (AVAudioEngine) and Android (AudioTrack). Zero-gap, zero-click loop playback for music production apps.
Homepage
Repository (GitHub)
View/report issues
Topics
#audio #loop #music #player #avaudiosession
Documentation
License
MIT (license)
Dependencies
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