AudioBufferSourceNode: loopStart property

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.


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.


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 = () => {
    const audioData = request.response;

      (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));

      (e) => console.error(`Error with decoding audio data: ${e.err}`),


// …

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

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


Web Audio API
# dom-audiobuffersourcenode-loopstart

Browser compatibility

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See also