AudioBufferSourceNode: playbackRate property

The playbackRate property of the AudioBufferSourceNode interface Is a k-rate 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 AudioParam whose 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

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 a slider control is used to change the playbackRate property value on the fly.

Note: You can run the example live (or view the source). Play the song and alter the playback rate for some fun results.

<input
  class="playback-rate-control"
  type="range"
  min="0.25"
  max="3"
  step="0.05"
  value="1" />
<span class="playback-rate-value">1.0</span>

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;
        source.buffer = myBuffer;
        source.playbackRate.value = playbackControl.value;
        source.connect(audioCtx.destination);
        source.loop = true;
      },

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

  request.send();
}

// wire up buttons to stop and play audio, and range slider control

play.onclick = () => {
  getData();
  source.start(0);
  play.setAttribute("disabled", "disabled");
  playbackControl.removeAttribute("disabled");
};

stop.onclick = () => {
  source.stop(0);
  play.removeAttribute("disabled");
  playbackControl.setAttribute("disabled", "disabled");
};

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

Specifications

Specification
Web Audio API
# dom-audiobuffersourcenode-playbackrate

Browser compatibility

BCD tables only load in the browser

See also