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AudioBufferSourceNode.loopStart

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

The loopStart property's default value is 0.

Syntax

AudioBufferSourceNode.loopStart = startOffsetInSeconds;

startOffsetInSeconds = AudioBufferSourceNode.loopStart;

Value

A floating-point number indicating the offset, in seconds, into the audio buffer at which each loop should begin during playback. This value is only used when the loop parameter is true.

Example

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.

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

function getData() {
  source = audioCtx.createBufferSource();
  request = new XMLHttpRequest();

  request.open('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.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.err});

  }

  request.send();
}

  ...

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

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

Specifications

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

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 14 12 25 No 15 6
Mobile
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support Yes 18 Yes 26 15 ? Yes

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/AudioBufferSourceNode/loopStart