WAV data of initially unknown length through StreamAudioSource is silent for prolonged periods of time before playing

[yaakovschectman]

Which API doesn't behave as documented, and how does it misbehave?
When an AudioPlayer plays from a StreamAudioSource that returns a response with a stream containing WAV PCM data and contentLength: null, sourceLength: null, offset: null to indicate that the overall length of the stream is not currently known, e.g. background sound that is continually generated, the audio is not played immediately. It may instead be played several minutes after the request completes, even for short amounts of data, e.g. 1 second long.

Minimal reproduction project

import 'dart:async';
import 'dart:math';
import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:just_audio/just_audio.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Chromatic scale',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Chromatic scale'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

const int _kRIFF = 0x52494646; // "RIFF"
const int _kWAVE = 0x57415645; // "WAVE"
const int _kfmt_ = 0x666d7420; // "fmt "
const int _kdata = 0x64617461; // "data"
const int _kMaxSize = 0xffffffff;
const int _kWavHeaderSize = 44;

// Generate a WAV header for a much-too-long file, as length may be unknown ahead of time, or infinite
int _writeWavHeader(ByteData dst, int hz, int nChannels, int nBytes) {
  dst.setUint32(0, _kRIFF, Endian.big);
  dst.setUint32(4, _kMaxSize, Endian.little);
  dst.setUint32(8, _kWAVE, Endian.big);
  dst.setUint32(12, _kfmt_, Endian.big);
  dst.setUint32(16, 16, Endian.little);
  dst.setUint16(20, 1, Endian.little);
  dst.setUint16(22, nChannels, Endian.little);
  dst.setUint32(24, hz, Endian.little);
  dst.setUint32(28, hz * nChannels * nBytes, Endian.little);
  dst.setUint16(32, nBytes * nChannels, Endian.little);
  dst.setUint16(34, nBytes * 8, Endian.little);
  dst.setUint32(36, _kdata, Endian.big);
  dst.setUint32(40, _kMaxSize, Endian.little);
  return _kWavHeaderSize;
}

// Audio source that generates PCM data and returns it with a WAV header
class StreamingSource extends StreamAudioSource {
  static const int _sampleRate = 44100;
  double frequency;

  StreamingSource([this.frequency = 440]);

  @override
  Future<StreamAudioResponse> request([int? start, int? end]) async {
    int t0 = start ?? 0;
    int nSecs = 1;
    int t1 = end ?? (_sampleRate * nSecs + _kWavHeaderSize);
    int len = t1 - t0;
    print('Requesting $start to $end, returning data of $len long.');
    assert(len >= _kWavHeaderSize);
    Uint8List data = Uint8List(len);
    int endOfHeader = _writeWavHeader(data.buffer.asByteData(), _sampleRate, 1, 1);
    for (int i = 0; i < data.length - endOfHeader; i++) {
      double samp = sin(i * 2 * pi * frequency / _sampleRate) * 0.5 + 0.5;
      data[endOfHeader + i] = (samp * 255).toInt();
    }
    return StreamAudioResponse(
      sourceLength: null,
      contentLength: null,
      offset: null,
      stream: Stream.fromIterable([data]),
      contentType: 'audio/wav',
      rangeRequestsSupported: true,
      );
  }

}

class _MyHomePageState extends State<MyHomePage> {
  late AudioPlayer _player;
  late StreamingSource _source;

  @override
  void initState() {
    super.initState();
    _player = AudioPlayer();
    _source = StreamingSource(440);
    _initPlayer();
  }

  Future<void> _initPlayer() async {
    await _player.pause();
    await _player.setAudioSource(_source, preload: false);
  }

  Future<void> _playTone() async {
    _source.frequency *= pow(2.0, 1.0/12);
    await _player.stop();
    await _player.seek(Duration.zero); // Stop and seek necesssary to request audio again
    await _player.play();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: _playTone,
        tooltip: 'Play',
        child: const Icon(Icons.add),
      ),
    );
  }
}

To Reproduce (i.e. user steps, not code)
Steps to reproduce the behavior:

1. Run the above sample.
2. Press the floating action button to call play

Actual behavior:
No audio is played for around 5 minutes, then the brief sine tone can be heard.

Error messages

[just_audio_windows] Called setVolume
[just_audio_windows] Called setSpeed
[just_audio_windows] Called setPitch
[just_audio_windows] Called setSkipSilence
[just_audio_windows] Called setLoopMode
[just_audio_windows] Called setShuffleMode
[just_audio_windows] Called play
[just_audio_windows] Called load
flutter: Requesting 0 to null, returning data of 44144 long.

Expected behavior
Once the audio data is requested and received from the Stream returned by StreamAudioSource.request, it should play a 1-second long sine tone of the current frequency.

Screenshots
N/A

Desktop (please complete the following information):

• OS: Win 10

Smartphone (please complete the following information):
N/A

Flutter SDK version

Doctor summary (to see all details, run flutter doctor -v):
[!] Flutter (Channel [user-branch], 3.12.0-1.0.pre.14, on Microsoft Windows [Version 10.0.19045.2965], locale en-US)
    ! Flutter version 3.12.0-1.0.pre.14 on channel [user-branch] at C:\src\flutter\flutter\flutter
      Currently on an unknown channel. Run `flutter channel` to switch to an official channel.
      If that doesn't fix the issue, reinstall Flutter by following instructions at https://flutter.dev/docs/get-started/install.
    ! Unknown upstream repository.
      Reinstall Flutter by following instructions at https://flutter.dev/docs/get-started/install.
[√] Windows Version (Installed version of Windows is version 10 or higher)
[√] Android toolchain - develop for Android devices (Android SDK version 33.0.0) 
[√] Chrome - develop for the web
[√] Visual Studio - develop Windows apps (Visual Studio Professional 2022 17.5.1)
[√] Android Studio (version 2021.3)
[√] VS Code (version 1.78.2)
[√] Connected device (3 available)
[√] Network resources

Additional context
The owner of the just_audio repo has stated that this is a bug with the native player.

[bdlukaa]

Hello! StreamAudioSource is, under the hood, a ProgressiveAudioSource (type progressive).

https://github.com/bdlukaa/just_audio_windows/blob/master/just_audio_windows/windows/player.hpp#L485-L487
https://github.com/ryanheise/just_audio/blob/b8edd0cee98b682f15f40a45d4fec325681d28f8/just_audio/lib/just_audio.dart#L2644-L2712

I would suspect just_audio takes a while to initialize the stream. Or does it initialize properly on other platforms?

What happens if contentLength: null, sourceLength: null, offset: null have a mock value assigned at start - such as 0 or 1?

The current implementation uses the method described in the Microsoft documentation:
https://learn.microsoft.com/en-us/windows/uwp/audio-video-camera/adaptive-streaming

[yaakovschectman]

Whenever contentLength is 0:
Errs:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: HttpException: Content size exceeds specified contentLength. 44144 bytes written while expected 0. [RIFFD¬[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: HttpException: Content size exceeds specified contentLength. 44144 bytes written while expected 0. [RIFFD¬flutter: Requesting 0 to null, returning data of 44144 long.

contentLength is null and offset is non-null:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Null check operator used on a null value
#0      _proxyHandlerForSource.handler (package:just_audio/just_audio.dart:3127:64)

contentLength is null and offset is null:
No sound is heard, as in the initial example.

On Chrome, audio can be heard immediately when these values are null.

[bdlukaa]

This is an issue with just_audio. We do not implement StreamAudioSource directly. Please report it on the just_audio repository. Thanks