index.md

---

title: AudioBufferSourceNode.loopStart
slug: Web/API/AudioBufferSourceNode/loopStart
page-type: web-api-instance-property
browser-compat: api.AudioBufferSourceNode.loopStart

---

{{ APIRef("Web Audio API") }}

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

The loopStart property's default value is 0.

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 {{domxref("AudioBufferSourceNode.loop", "loop")}} parameter is true.

Examples

In this example, the {{domxref("BaseAudioContext/decodeAudioData", "AudioContext.decodeAudioData()")}} function is used to decode an audio track and put it into an {{domxref("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();

  request.open("GET", "viper.ogg", true);
  request.responseType = "arraybuffer";

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

    audioCtx.decodeAudioData(
      audioData,
      (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));
      },

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

  request.send();
}

// …

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

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

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Web Audio API

• Using the Web Audio API