coast_audio 0.0.4

A cross-platform audio processing library written in dart

Overview

coast_audio is a high performance audio processing library written in dart.
This package aims to provide low-level audio functionalities.

Features

• PCM Format Management
• Audio Buffer
• Ring Buffer
• Encoding and Decoding
• Wave Generation
  • Sine
  • Triangle
  • Square
  • Sawtooth
• Effects
  • Delay
  • Mixer
  • Volume

Audio Format

AudioFormat contains sample rate, channels, sample format information.
You may usually use this class to allocate audio buffers or provide information to audio nodes.

Audio Processing

You can use AudioNode subclasses to produce or process an audio buffer.
There are two kinds of nodes are available.

• Data Source Node
  • produces the audio data and write to buffer
  • usually extends the DataSourceNode abstract class
• Processor Node
  • manipulate, consume, and/or passthrough the audio buffer to the connected node
  • usually extends the SingleInOutNode with ProcessorNodeMixin.

For example, FunctionNode can produce wave data based on the supplied function, which extends the DataSourceNode.
It has one outputBus so you can read audio data from it.

Below code generates 48000hz stereo sine wave.

import 'package:coast_audio/coast_audio.dart';

const format = AudioFormat(sampleRate: 48000, channels: 2); // sampleFormat is float32 by default.
final functionNode = FunctionNode(
  function: const SineFunction(),
  frequency: 440,
);
final frames = AllocatedAudioFrames(
  length: 1024,
  format: format,
);

// Read to the buffer and access the audio data in 32bit floating point format.
frames.acquireBuffer((buffer) {
  final framesRead = functionNode.outputBus.read(buffer);
  final floatList = buffer.limit(framesRead).asFloatListView();
  // Do whatever you want!
});

// Dispose the buffer.
frames.dispose();

coast_audio has various kinds of built-in nodes.
Each node has one or more busses to connect with other nodes.

GraphNode

To build your own audio graph, use the GraphNode class.
GraphNode has connect and connectEndpoint methods to connect between node's bus.

Example: mixing multiple nodes and write to wav file

See the example code.

Audio Buffer

AudioFrames

By using AudioFrames subclasses, you can manage audio buffers easily.
In most cases, you should use the AllocatedAudioFrames class.

AudioFrames have lock and unlock methods to access the AudioBuffer which contains the pointer to raw audio data.

final frames = AllocatedAudioFrames(length: 1024, format: format);
final buffer = frames.lock();
try {
  // Use the buffer.pBuffer to access the raw audio data.
  // Or you can call buffer.asFloatListView() to acquire the view of list data.
} finally {
  frames.unlock();
}
frames.dispose();

Or you can use acquireBuffer to lock & unlock audio buffer automatically.

frames.acquireBuffer((niffer) {
  // frames will be unlocked when the callback method is finished.
});

AudioBuffer has offset and limit methods to retrieve the sub view of AudioBuffer.

final frames = AllocatedAudioFrames(length: 1024, format: format);
final buffer = frames.lock();
final subBuffer1 = buffer.limit(128); // Takes first 128 frames.
final subBuffer2 = buffer.offset(128); // Skips first 128 frames.
frames.unlock();
frames.dispose(); // subBuffer1 and subBuffer2 will be invalidated too.

RingBuffer

coast_audio provides ring buffer implementations.
You can use the FrameRingBuffer to manage audio frames, or use the RingBuffer to manage data in binary format.

Audio Decoder

When you want to read audio data from a file, use the AudioFileDataSource class and pass it to the AudioDecoder subclasses.
Currently, this package only provides WavAudioDecoder which can decode wav audio data from the data source.

final dataSource = AudioFileDataSource(file: File('test.wav'), mode: FileMode.read);
final decoder = WavAudioDecoder(dataSource: dataSource);

final frames = AllocatedAudioFrames(length: 512, format: decoder.format);
frames.acquireBuffer((buffer) {
  final result = decoder.decode(destination: buffer);
  final readBuffer = buffer.limit(result.frames);
  // `readBuffer` is now contains decoded audio data.
});
frames.dispose();
dataSource.dispose();

If you want to read a mp3 or flac file, use the coast_audio_miniaudio package instead.
It has MabAudioDecoder class to read audio data from files.

Then, you can initialize the DecoderNode to decode audio data in real-time.