CODEWITHSUNDEEP
javascripthtmlwebkitaudiocontext
ronag
ronag

Reputation: 51245

Custom MediaStream

I'm receive raw float32 audio through websockets and would like to playback this in the browser. From my understanding I would need to to use MediaStream API for this. However, I cannot find a way to create a MediaStream which I can append data buffers to.

What is the proper way to achieve this?

I'm trying something like this:

    var context = new AudioContext();

    context.sampleRate = 48000;

    var stream = null; // ????

    var source = context.createMediaStreamSource(stream);
    source.connect(context.destination);
    source.start(0);

    socket.onmessage = function (event) {
        stream.appendBuffer(new Float32Array(event.data)); // ????
    };

Upvotes: 24

Views: 5861

Answers (2)

daz
daz

Reputation: 784

You should use the AudioBuffers to read sound from the buffers from the websocket and play it.

var context = new AudioContext();
var sampleRate = 48000;
var startAt = 0;

socket.onmessage = function (event) {
    var floats = new Float32Array(event.data);
    var source = context.createBufferSource();
    var buffer = context.createBuffer(1, floats.length, sampleRate);
    buffer.getChannelData(0).set(floats);
    source.buffer = buffer;
    source.connect(context.destination);
    startAt = Math.max(context.currentTime, startAt);
    source.start(startAt);
    startAt += buffer.duration;
};

This plays the music from a websocket.

To convert an AudioBuffer into a MediaStream, use AudioContext.createMediaStreamDestination(). Connect the BufferSource to it to make the custom MediaStream based on the buffer's data.

var data = getSound(); // Float32Array;
var sampleRate = 48000;
var context = new AudioContext();

var streamDestination = context.createMediaStreamDestination();
var buffer = context.createBuffer(1, data.length, sampleRate);
var source = context.createBufferSource();

buffer.getChannelData(0).set(data);
source.buffer = buffer;
source.connect(streamDestination);
source.loop = true;
source.start();

var stream = streamDestination.stream;

This reads audio from the data array and converts it into a MediaStream.

Upvotes: 7

C.Vergnaud
C.Vergnaud

Reputation: 877

Regarding decoding, audioContext from the window object should do the job.

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();

and then 

audioCtx.decodeAudioData(audioData, function(buffer) {

directly on the binary array.

Regarding communication, I'd rather use XMLHttpRequest (a low level function and old) and using the response directly.

This is a pretty good function made by MDM guys (I updated the url of the ogg file so you can test it directly) :

function getData() {
  source = audioCtx.createBufferSource();
  request = new XMLHttpRequest();
  request.open('GET', 'https://raw.githubusercontent.com/mdn/webaudio-examples/master/decode-audio-data/viper.ogg', true);
  request.responseType = 'arraybuffer';
  request.onload = function() {
    var audioData = request.response;
    audioCtx.decodeAudioData(audioData, function(buffer) {
        myBuffer = buffer;
        songLength = buffer.duration;
        source.buffer = myBuffer;
        source.playbackRate.value = playbackControl.value;
        source.connect(audioCtx.destination);
        source.loop = true;
        loopstartControl.setAttribute('max', Math.floor(songLength));
        loopendControl.setAttribute('max', Math.floor(songLength));
      },
      function(e){"Error with decoding audio data" + e.error});
  }
  request.send();
}

the full source code is here :

https://raw.githubusercontent.com/mdn/webaudio-examples/master/decode-audio-data/index.html

Upvotes: -1

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