Flutter low level audio plugin using SoLoud library

Flutter low level audio plugin using SoLoud library with miniaudio backend and FFI. It provides player, basic capture from microphone, 3D audio and more.

Linux	Windows	Android	MacOS	iOS	web
💙	💙	💙	💙	💙	😭

🌐 Supported on Linux, Windows, Mac, Android, and iOS

🎤 Player and capture audio from microphone (no recording)

🎶 3D audio with doppler effect

🎚️ Faders, oscillators and audio effects like echo, freeverb, robotizer, equalizer, bassboost

🎙️ Multiple voices, capable of playing different sounds simultaneously or even repeating the same sound multiple times on top of each other

💬 Includes a simple speech synthesizer

🔊 Supports various common formats such as 8, 16, and 32-bit WAVs, floating point WAVs, OGG, MP3, and FLAC

🎚️ Enables real-time retrieval of audio FFT and wave data

Overview

The flutter_soloud plugin utilizes a forked repository of SoLoud, where the miniaudio audio backend has been updated and is located in src/soloud/src/backend/miniaudio

For information regarding the SoLoud license, please refer to this link.

There are 5 examples: (to use microphone on MacOs or iOS you should add audio input permission in the example app)

The 1st is a simple use-case to show how to play a sound and how to activate the capture.

The 2nd aims to show a visualization of frequencies and wave data. The file [Visualizer.dart] uses getAudioTexture2D to store new audio data into audioData on every tick.

The video below illustrates how the data is then converted to an image (the upper widget) and sent to the shader (the middle widget). The bottom widgets use FFT data on the left and wave data represented with a row of yellow vertical containers with the height taken from audioData on the right.

The getAudioTexture2D returns an array of 512x256. Each row contains 256 Floats of FFT data and 256 Floats of wave data, making it possible to write a shader like a spectrogram (shader #8) or a 3D visualization (shader #9).

Shaders from 1 to 7 are using just 1 row of the audioData. Therefore, the texture generated to feed the shader should be 256x2 px. The 1st row represents the FFT data, and the 2nd represents the wave data.

Since many operations are required for each frame, the CPU and GPU can be under stress, leading to overheating of a mobile device. It seems that sending an image (with setImageSampler()) to the shader is very expensive. You can observe this by disabling the shader widget.

soloud6.mp4

The 3rd example demonstrates how to manage sounds using their handles: every sound should be loaded before it can be played. Loading a sound can take some time and should not be done during gameplay, for instance, in a game. Once a sound is loaded, it can be played, and every instance of that same audio will be identified by its handle.

The example shows how you can have background music and play a fire sound multiple times.

soloud6-B.mp4

The 4th example shows how to enance audio with 3D capabilities. There is a circle where the listener is placed in the center and a moving siren audio is represented by a little circle which is automatically animated or can be moved by mouse gesture. The sound volume fades off at the circonference. There is also a doppler effect that can be turned off.

soloud8-3Daudio.mp4

The 5th example shows how to generete [SoundProps] key sounds. There is a handy tool method to generate the 12 key notes of a given octave. A widget to play them can be used with the touch or a keyboard. Different types of waveforms can be chosen including square,saw,sin,triangle,bounce,jaws,humps,fSquare and fSaw. There are also simple knobs to adjust faders and oscillators. Other knobs to add/remove audio effects.

soloud9-waveform-B.mp4

Usage

The Player

First of all, AudioIsolate must be initialized:

Future<bool> start() async{
  final value = SoLoud().startIsolate();
  if (value == PlayerErrors.noError) {
    debugPrint('isolate started');
    return true;
  } else {
    debugPrint('isolate starting error: $value');
    return false;
  }
}

When succesfully started a sound can be loaded:

Future<SoundProps?> loadSound(String completeFileName) {
  final load = await SoLoud().loadFile(completeFileName);
  if (load.error != PlayerErrors.noError) return null;
  return load.sound;
}

There are 3 convenient methods that can be used instead in the [SoloudLoadingTool] class:

• Future<SoundProps?> loadFromAssets(String path)
• Future<SoundProps?> loadFromFile(String path)
• Future<SoundProps?> loadFromUrl(String url)

The [SoundProps] class:

class SoundProps {
  SoundProps(this.soundHash);

  // the [hash] returned by [loadFile]
  final int soundHash;

  /// handles of this sound. Multiple instances of this sound can be
  /// played, each with their unique handle
  List<int> handle = [];

  /// the user can listed ie when a sound ends or key events (TODO)
  StreamController<StreamSoundEvent> soundEvents = StreamController.broadcast();
}

soundHash and handle list are then used to call many methods in the AudioIsolate() class.

warning: when you call a load* method, in return you will get a SoundProps. This is the reference to the sound which is used by SoLoud and need to be disposed when is no more needed. When you play a SoundsProps, intstead a new handle, to identify the new playing instance, is created and added to SoundProps.handle list. This let you play the sound as many times you want without calling a load* method again which can be laggy. To dispose a sound call you should call Soloud().disposeSound or Soloud().disposeAllSounds

Capture from microphone

Start the capture

SoLoud().initCapture();
SoLoud().startCapture();

now it's possible to get audio data. When the mic is no more needed, it can be stopped:

SoLoud().stopCapture();

With the audio data it will be simple to do something like in the 1st example:

soloud7-capture.mp4

The AudioIsolate instance

The AudioIsolate instance has the duty of receiving commands and sending them to a separate Isolate, while returning the results to the main UI isolate.

Player methods

Function	Returns	Params	Description
startIsolate	PlayerErrors	-	Start the audio isolate and listen for messages coming from it.
stopIsolate	bool	-	Stop the loop, stop the engine, and kill the isolate. Must be called when there is no more need for the player or when closing the app.
isIsolateRunning	bool	-	Return true if the audio isolate is running.
initEngine	PlayerErrors	-	Initialize the audio engine. Defaults are: Sample rate 44100, buffer 2048, and Miniaudio audio backend.
dispose	-	-	Stop the audio engine.
loadFile	({PlayerErrors error, SoundProps? sound})	String fileName, LoadMode mode = LoadMode.memory	Load a new sound to be played once or multiple times later. If mode = LoadMode.disk, seek will have lags with MP3s.
play	({PlayerErrors error, SoundProps sound, int newHandle})	int soundHash, { double volume = 1, double pan = 0, bool paused = false, }	Play an already loaded sound identified by [sound].
speechText	({PlayerErrors error, SoundProps sound})	String textToSpeech	Speech from the given text.
pauseSwitch	PlayerErrors	int handle	Pause or unpause an already loaded sound identified by [handle].
getPause	({PlayerErrors error, bool pause})	int handle	Get the pause state of the sound identified by [handle].
setRelativePlaySpeed	PlayerErrors	int handle, double speed	Set a sound's relative play speed.
getRelativePlaySpeed	({PlayerErrors error, double speed})	int handle	Return the current play speed.
stop	PlayerErrors	int handle	Stop an already loaded sound identified by [handle] and clear it.
disposeSound	PlayerErrors	int handle	Stop ALL handles of the already loaded sound identified by [soundHash] and dispose it.
getLooping	({PlayerErrors error, bool isLooping})	-	Query whether a sound is set to loop.
setLooping	-	int handle, bool enable	This function can be used to set a sample to play on repeat, instead of just playing once.
getLoopPoint	({PlayerErrors error, double time})	-	Get sound loop point value.
setLoopPoint	PlayerErrors	SoundHandle handle, double time	Set sound loop point value.
getLength	({PlayerErrors error, double length})	int soundHash	Get the sound length in seconds.
seek	PlayerErrors	int handle, double time	Seek playing in seconds. WARNING: when loading an MP3 file with mode = LoadMode.disk, the seek is laggy. This should not happens with FLACs, OGGs and WAVs.
getPosition	({PlayerErrors error, double position})	int handle	Get the current sound position in seconds.
getVolume	({PlayerErrors error, double volume})	int handle	Get current [handle] volume.
setVolume	({PlayerErrors error, double volume})	int handle, double volume	set [handle] volume.
getIsValidVoiceHandle	({PlayerErrors error, bool isValid})	int handle	Check if a handle is still valid.
setVisualizationEnabled	-	bool enabled	Enable or disable getting data from getFft, getWave, getAudioTexture*.
getVisualizationEnabled	({PlayerErrors error, bool isEnabled})	-	Get the state of visualization flag.
getFft	-	Pointer<Float> fft	Returns a 256 float array containing FFT data.
getWave	-	Pointer<Float> wave	Returns a 256 float array containing wave data (magnitudes).
getAudioTexture	-	Pointer<Float> samples	Returns in samples a 512 float array. - The first 256 floats represent the FFT frequencies data [>=0.0]. - The other 256 floats represent the wave data (amplitude) [-1.0~1.0].
getAudioTexture2D	-	Pointer<Pointer<Float>> samples	Return a floats matrix of 256x512. Every row is composed of 256 FFT values plus 256 wave data. Every time is called, a new row is stored in the first row and all the previous rows are shifted up (the last will be lost).
setFftSmoothing	-	double smooth	Smooth FFT data. When new data is read and the values are decreasing, the new value will be decreased with an amplitude between the old and the new value. This will result in a less shaky visualization. 0 = no smooth 1 = full smooth The new value is calculated with: newFreq = smooth * oldFreq + (1 - smooth) * newFreq

Waveform

Function	Returns	Params	Description
loadWaveform	({PlayerErrors error, SoundProps? sound})	WaveForm waveform bool superWave double scale double detune	Load a new sound to be played.
setWaveform	PlayerErrors	SoundProps sound WaveForm newWaveform	Set a new waveform for the [sound].
setWaveformScale	PlayerErrors	SoundProps sound double newScale	Set a new scale for the [sound] (only if [superWave] is true).
setWaveformDetune	PlayerErrors	SoundProps sound double newDetune	Set a new detune for the [sound] (only if [superWave] is true).
setWaveformFreq	PlayerErrors	SoundProps sound double newFreq	Set a new frequency for the [sound].
setWaveformSuperWave	PlayerErrors	SoundProps sound bool superwave	Set to compute superwave for the [sound].

enum WaveForm

Name	Description
square	Raw, harsh square wave
saw	Raw, harsh saw wave
sin	Sine wave
triangle	Triangle wave
bounce	Bounce, i.e, abs(sin())
jaws	Quater sine wave, rest of period quiet
humps	Half sine wave, rest of period quiet
fSquare	"Fourier" square wave; less noisy
fSaw	"Fourier" saw wave; less noisy

Audio FXs, faders and oscillators methods

These methods add audio effects to sounds. Faders and oscillators are binded to sound handles, so they need [SoundProps.handle] as first parameter. Audio FXs like echo, freeverb, bassboost etc, are working on the output, so they can set anytime while playing something.

Function	Returns	Params	Description
fadeGlobalVolume	PlayerErrors error	double to, double time	Smoothly change the global volume over specified time.
fadeVolume	PlayerErrors error	int handle, double to, double time	Smoothly change a channel's volume over specified time.
fadePan	PlayerErrors error	int handle, double to, double time	Smoothly change a channel's pan setting over specified time.
fadeRelativePlaySpeed	PlayerErrors error	int handle, double to, double time	Smoothly change a channel's relative play speed over specified time.
schedulePause	PlayerErrors error	int handle, double time	After specified time, pause the channel.
scheduleStop	PlayerErrors error	int handle, double time	After specified time, stop the channel.
oscillateVolume	PlayerErrors error	int handle, double from, double to, double time	Smoothly change a channel's pan setting over specified time.
oscillatePan	PlayerErrors error	int handle, double from, double to, double time	Set fader to oscillate the panning at specified frequency.
oscillateRelativePlaySpeed	PlayerErrors error	int handle, double from, double to, double time	Set fader to oscillate the relative play speed at specified frequency.
oscillateGlobalVolume	PlayerErrors error	double from, double to, double time	Set fader to oscillate the global volume at specified frequency.
isFilterActive	({PlayerErrors error, int index})	FilterType filterType	Check if the given filter is active or not.
getFilterParamNames	({PlayerErrors error, List names})	FilterType filterType	Get parameters names of the given filter.
addGlobalFilter	PlayerErrors	FilterType filterType	Add the filter [filterType].
removeGlobalFilter	PlayerErrors	FilterType filterType	Remove the filter [filterType].
setFxParams	PlayerErrors	FilterType filterType, int attributeId, double value	Set the effect parameter with id [attributeId] of [filterType] with [value] value.
getFxParams	PlayerErrors	FilterType filterType, int attributeId	Get the effect parameter with id [attributeId] of [filterType].

enum FilterType

Name
biquadResonantFilter
eqFilter
echoFilter
lofiFilter
flangerFilter
bassboostFilter
waveShaperFilter
robotizeFilter
freeverbFilter

There are also conveninet const to easily access effect parameter like filter name, param names, mins values, max values and defaults:

fxEq, fxEcho, fxLofi, fxFlanger, fxBassboost, fxWaveShaper, fxRobotize, fxFreeverb.

3D audio methods

Function	Returns	Params	Description
play3d	int handle	int soundHash, double posX, double posY, double posZ, {double velX = 0, double velY = 0, double velZ = 0, double volume = 1, bool paused = false}	play3d() is the 3d version of the play() call. Returns the handle of the sound, 0 if error
set3dSoundSpeed	-	double speed	Since SoLoud has no knowledge of the scale of your coordinates, you may need to adjust the speed of sound for these effects to work correctly. The default value is 343, which assumes that your world coordinates are in meters (where 1 unit is 1 meter), and that the environment is dry air at around 20 degrees Celsius.
get3dSoundSpeed	double	-	Get the sound speed.
set3dListenerParameters	-	double posX,double posY, double posZ, double atX, double atY, double atZ, double upX, double upY, double upZ, double velocityX, double velocityY, double velocityZ	You can set the position, at-vector, up-vector and velocity parameters of the 3d audio listener with one call.
set3dListenerPosition	-	double posX, double posY, double posZ	Get the sound speed.
set3dListenerAt	-	double atX, double atY, double atZ	You can set the "at" vector parameter of the 3d audio listener.
set3dListenerUp	-	double upX, double upY, double upZ	You can set the "up" vector parameter of the 3d audio listener.
set3dListenerVelocity	-	double velocityX, double velocityY, double velocityZ	You can set the listener's velocity vector parameter.
set3dSourceParameters	-	int handle, double posX, double posY, double posZ, double velocityX, double velocityY, double velocityZ	You can set the position and velocity parameters of a live 3d audio source with one call.
set3dSourcePosition	-	int handle, double posX, double posY, double posZ	You can set the position parameters of a live 3d audio source.
set3dSourceVelocity	-	int handle, double velocityX, double velocityY, double velocityZ	You can set the velocity parameters of a live 3d audio source.
set3dSourceMinMaxDistance	-	int handle, double minDistance, double maxDistance	You can set the minimum and maximum distance parameters of a live 3d audio source.
set3dSourceAttenuation	-	int handle, int attenuationModel, double attenuationRolloffFactor	You can change the attenuation model and rolloff factor parameters of a live 3d audio source. See https://solhsa.com/soloud/concepts3d.html
set3dSourceDopplerFactor	-	int handle, double dopplerFactor	You can change the doppler factor of a live 3d audio source. See https://solhsa.com/soloud/concepts3d.html

The PlayerErrors enum:

name	description
noError	No error
invalidParameter	Some parameter is invalid
fileNotFound	File not found
fileLoadFailed	File found, but could not be loaded
dllNotFound	DLL not found, or wrong DLL
outOfMemory	Out of memory
notImplemented	Feature not implemented
unknownError	Other error
backendNotInited	Player not initialized
nullPointer	null pointer. Could happens when passing a non initialized pointer (with calloc()) to retrieve FFT or wave data
soundHashNotFound	The sound with specified hash is not found
fileAlreadyLoaded	The sound file has already been loaded
isolateAlreadyStarted	Audio isolate already started
isolateNotStarted	Audio isolate not yet started
engineNotInited	Engine not yet started

AudioIsolate() has a StreamController which can be used, for now, only to know when a sound handle reached the end:

StreamSubscription<StreamSoundEvent>? _subscription;
void listedToEndPlaying(SoundProps sound) {
  _subscription = sound!.soundEvents.stream.listen(
    (event) {
      /// Here the [event.handle] of [sound] has naturally finished
      /// and [sound.handle] doesn't contains [envent.handle] anymore.
      /// Not passing here when calling [SoLoud().stop()]
      /// or [SoLoud().disposeSound()]
    },
  );
}

it has also a StreamController to monitor when the engine starts or stops:

SoLoud().audioEvent.stream.listen(
  (event) {
    /// event is of [AudioEvent] enum type:
    /// [AudioEvent.isolateStarted] the player is started and sounds can be played
    /// [AudioEvent.isolateStopped] player stopped
    /// [captureStarted] microphone is active and audio data can be read
    /// [captureStopped] microphone stopped
  },
);

Capture methods

Function	Returns	Params	Description
listCaptureDevices	CaptureDevice	-	List available input devices. Useful on desktop to choose which input device to use.
initCapture	CaptureErrors	-	Initialize input device with [deviceID] Return [CaptureErrors.captureNoError] if no error.
isCaptureInitialized	bool	-	Get the status of the device.
isCaptureStarted	bool	-	Returns true if the device is capturing audio.
stopCapture	CaptureErrors	-	Stop and deinit capture device.
startCapture	CaptureErrors	-	Start capturing audio data.
getCaptureAudioTexture2D	CaptureErrors	-	Return a floats matrix of 256x512 Every row are composed of 256 FFT values plus 256 of wave data. Every time is called, a new row is stored in the first row and all the previous rows are shifted up (the last one will be lost).
setCaptureFftSmoothing	CaptureErrors	double smooth	Smooth FFT data. When new data is read and the values are decreasing, the new value will be decreased with an amplitude between the old and the new value. This will resul on a less shaky visualization. [smooth] must be in the [0.0 ~ 1.0] range. 0 = no smooth 1 = full smooth the new value is calculated with: newFreq = smooth * oldFreq + (1 - smooth) * newFreq

Logging

The flutter_soloud package logs everything (from severe warnings to fine debug messages) using the standard logging package.

See the example's lib/main.dart to see how to capture these logs. For example:

import 'dart:developer' as dev;

void main() {
  // Cut-off for messages. (Lower levels than INFO will be discarded.)
  Logger.root.level = Level.FINE;
  Logger.root.onRecord.listen((record) {
    // Forward logs to the console.
    dev.log(
      record.message,
      time: record.time,
      level: record.level.value,
      name: record.loggerName,
      zone: record.zone,
      error: record.error,
      stackTrace: record.stackTrace,
    );
    // TODO: if needed, forward to Sentry.io, Crashlytics, etc.
  });

  runApp(const MyApp());
}

If you don't set up a listener like the one above, there will be no logging from the package.

See the logging package's documentation to learn more about its functionality.

Contribute

To use native code, bindings from Dart to C/C++ are needed. To avoid writing these manually, they are generated from the header file (src/ffi_gen_tmp.h) using package:ffigen and temporarily stored in lib/flutter_soloud_FFIGEN.dart. You can generate the bindings by running dart run ffigen.

Since I needed to modify the generated .dart file, I followed this flow:

1. Copy the function declarations to be generated into src/ffi_gen_tmp.h.
2. The file lib/flutter_soloud_FFIGEN.dart will be generated.
3. Copy the relevant code for the new functions from lib/flutter_soloud_FFIGEN.dart into lib/flutter_soloud_bindings_ffi.dart.

Additionally, I have forked the SoLoud repository and made modifications to include the latest Miniaudio audio backend. This backend is in the [new_miniaudio] branch of my fork and is set as the default.

Project structure

This plugin uses the following structure:

• lib: Contains the Dart code that defines the API of the plugin relative to all platforms.

• src: Contains the native source code. Linux, Android and Windows have their own CmakeFile.txt file in their own subdir to build the code into a dynamic library.

• src/soloud: contains the SoLoud sources of my fork

Debugging

I have provided the necessary settings in the .vscode directory for debugging native C++ code on both Linux and Windows. To debug on Android, please use Android Studio and open the project located in the example/android directory. However, I am not familiar with the process of debugging native code on Mac and iOS.

Logging

When debugging the package using the example/ app, you might want to change the logging level to something more granular. For example, in main():

// Capture even the finest log messages.
Logger.root.level = Level.ALL;

One thing that's missing (as of March 2024) is logging from inside the audio isolate. We'd have to send logs to the main isolate through an event, which might be too expensive and brittle. Feel free to use debugPrint in audio_isolate.dart when working on the package. Just make sure to delete those calls before submitting pull requests. We don't want to pollute developers' console outputs.

Linux

If you encounter any glitches, they might be caused by PulseAudio. To troubleshoot this issue, you can try disabling PulseAudio within the linux/src.cmake file. Look for the line add_definitions(-DMA_NO_PULSEAUDIO) and uncomment it (now it is the default behavior).

Android

The default audio backend is miniaudio, which will automatically select the appropriate audio backend based on your Android version:

• AAudio with Android 8.0 and newer.
• OpenSL|ES for older Android versions.

Windows

For Windows users, SoLoud utilizes Openmpt through a DLL, which can be obtained from https://lib.openmpt.org/. If you wish to use this feature, install the DLL and enable it by modifying the first line in windows/src.cmake.

Openmpt functions as a module-playing engine, capable of replaying a wide variety of multichannel music formats (669, amf, ams, dbm, digi, dmf, dsm, far, gdm, ice, imf, it, itp, j2b, m15, mdl, med, mid, mo3, mod, mptm, mt2, mtm, okt, plm, psm, ptm, s3m, stm, ult, umx, wow, xm). Additionally, it can load wav files and may offer better support for wav files compared to the stand-alone wav audio source.

iOS

On the simulator, the Impeller engine doesn't work (20 Lug 2023). To disable it, run the following command: flutter run --no-enable-impeller Unfortunately, I don't have a real device to test it.

Web

I put in a lot of effort to make this to work on the web! :( I have successfully compiled the sources with Emscripten. Inside the web directory, there's a script to automate the compiling process using the CmakeLists.txt file. This will generate libflutter_soloud_web_plugin.wasm and libflutter_soloud_web_plugin.bc.

Initially, I tried using the wasm_interop plugin, but encountered errors while loading and initializing the Module.

Then, I attempted using web_ffi, but it seems to have been discontinued because it only supports the old dart:ffi API 2.12.0, which cannot be used here.

TODOs

Many things can still be done.

• Record from microphone to audio file.
• Since the load audio file feature uses the memory to store all audio data (see #26) to have no lags when start playing (useful with game sounds), make it possible to use Soloud::wavStream
• The FFT data doesn't match my expectations. Some work still needs to be done on Analyzer::calcFFT() in src/analyzer.cpp.

flutter_soloud spectrum	audacity spectrum

For now, only a small portion of the possibilities offered by SoLoud have been implemented. Look here.

• audio filter effects
• 3D audio ✅
• TED and SID soundchip simulator (Commodore 64/plus)
• noise and waveform generation ✅ and much more I think!