flutter_gapless_loop 0.0.1 
flutter_gapless_loop: ^0.0.1 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 '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 ${(_pan * 100).toStringAsFixed(0)}%',
style: Theme.of(context).textTheme.bodySmall,
),
],
),
],
),
),
);
}
}
class _BpmCard extends StatelessWidget {
const _BpmCard({required this.result, required this.isReady});
final BpmResult? result;
final bool isReady;
@override
Widget build(BuildContext context) {
if (!isReady) {
return const Text('Load a file to see BPM detection results.',
style: TextStyle(color: Colors.grey));
}
if (result == null) {
return const Row(
children: [
SizedBox(width: 16, height: 16, child: CircularProgressIndicator(strokeWidth: 2)),
SizedBox(width: 8),
Text('Detecting BPM...'),
],
);
}
final r = result!;
if (r.bpm == 0.0) {
return const Text('No BPM detected (audio too short or silent).',
style: TextStyle(color: Colors.grey));
}
final confidencePct = (r.confidence * 100).toStringAsFixed(0);
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
'${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),
],
);
}
}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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