AudioBufferSourceNode: playbackRate property

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

The playbackRate property of the {{ domxref("AudioBufferSourceNode") }} interface Is a k-rate {{domxref("AudioParam")}} that defines the speed at which the audio asset will be played.

A value of 1.0 indicates it should play at the same speed as its sampling rate, values less than 1.0 cause the sound to play more slowly, while values greater than 1.0 result in audio playing faster than normal. The default value is 1.0. When set to another value, the AudioBufferSourceNode resamples the audio before sending it to the output.

Value

An {{domxref("AudioParam")}} whose {{domxref("AudioParam.value", "value")}} is a floating-point value indicating the playback rate of the audio as a decimal proportion of the original sampling rate.

Consider a sound buffer containing audio sampled at 44.1 kHz (44,100 samples per second). Let's see what a few values of playbackRate do:

• A playbackRate of 1.0 plays the audio at full speed, or 44,100 Hz.
• A playbackRate of 0.5 plays the audio at half speed, or 22,050 Hz.
• A playbackRate of 2.0 doubles the audio's playback rate to 88,200 Hz.

Examples

Setting playbackRate

In this example, when the user presses "Play", we load an audio track, decode it, and put it into an {{domxref("AudioBufferSourceNode")}}.

The example then sets the loop property to true, so the track loops, and plays the track.

The user can set the playbackRate property using a range control.

[!NOTE] You can run the full example live (or view the source.)

let audioCtx;
let buffer;
let source;

const play = document.getElementById("play");
const stop = document.getElementById("stop");

const playbackControl = document.getElementById("playback-rate-control");
const playbackValue = document.getElementById("playback-rate-value");

async function loadAudio() {
  try {
    // Load an audio file
    const response = await fetch("rnb-lofi-melody-loop.wav");
    // Decode it
    buffer = await audioCtx.decodeAudioData(await response.arrayBuffer());
  } catch (err) {
    console.error(`Unable to fetch the audio file. Error: ${err.message}`);
  }
}

play.addEventListener("click", async () => {
  if (!audioCtx) {
    audioCtx = new AudioContext();
    await loadAudio();
  }
  source = audioCtx.createBufferSource();
  source.buffer = buffer;
  source.connect(audioCtx.destination);
  source.loop = true;
  source.playbackRate.value = playbackControl.value;
  source.start();
  play.disabled = true;
  stop.disabled = false;
  playbackControl.disabled = false;
});

stop.addEventListener("click", () => {
  source.stop();
  play.disabled = false;
  stop.disabled = true;
  playbackControl.disabled = true;
});

playbackControl.oninput = () => {
  source.playbackRate.value = playbackControl.value;
  playbackValue.textContent = playbackControl.value;
};

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Using the Web Audio API
• Web Audio API