The loopStart property of the AudioBufferSourceNode interface is a double value indicating, in seconds, where in the AudioBuffer the restart of the play must happen.

The loopStart property's default value is 0.


var source = audioCtx.createBufferSource();
source.loopStart = 3;


A double.


In this example, the AudioContext.decodeAudioData function is used to decode an audio track and put it into an AudioBufferSourceNode. Buttons are provided to play and stop the audio playback, and slider controls are used to change the playbackRate, loopStart and loopEnd properties on the fly.

When the audio is played to the end, it loops, but you can control how long the loops last by altering loopStart and loopEnd. For example, if you set their values to 20 and 25, respectively, the audio will start to loop between 20 and 25 seconds in to the track.

Note: For a full working example, see this code running live, or view the source.

function getData() {
  source = audioCtx.createBufferSource();
  request = new XMLHttpRequest();'GET', '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.loop = true;

        loopstartControl.setAttribute('max', Math.floor(songLength));
        loopendControl.setAttribute('max', Math.floor(songLength));

      function(e){"Error with decoding audio data" + e.err});




loopstartControl.oninput = function() {
  source.loopStart = loopstartControl.value;
  loopstartValue.innerHTML = loopstartControl.value;

loopendControl.oninput = function() {
  source.loopEnd = loopendControl.value;
  loopendValue.innerHTML = loopendControl.value;


Specification Status Comment
Web Audio API
The definition of 'loopStart' in that specification.
Working Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 14 webkit 23 Not supported 15 webkit
22 (unprefixed)
6 webkit
Feature Android Chrome Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support Not supported 28 webkit 25 1.2 Not supported Not supported webkit

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API AudioBufferSourceNode loopStart Property Reference Référence Web Audio API