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.
Syntax
AudioBufferSourceNode.playbackRate.value = playbckRateProportion;
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.
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 a slider control is used to change the playbackRate
property value on the fly.
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 = function() { var audioData = request.response; audioCtx.decodeAudioData(audioData, function(buffer) { myBuffer = buffer; source.buffer = myBuffer; source.playbackRate.value = playbackControl.value; source.connect(audioCtx.destination); source.loop = true; }, function(e){"Error with decoding audio data" + e.err}); } request.send(); } // wire up buttons to stop and play audio, and range slider control play.onclick = function() { getData(); source.start(0); play.setAttribute('disabled', 'disabled'); playbackControl.removeAttribute('disabled'); } stop.onclick = function() { source.stop(0); play.removeAttribute('disabled'); playbackControl.setAttribute('disabled', 'disabled'); } playbackControl.oninput = function() { source.playbackRate.value = playbackControl.value; playbackValue.innerHTML = playbackControl.value; }
Specification
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'playbackRate' in that specification. |
Working Draft |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|---|
Basic support | 14 webkit | (Yes) | 23 | No support | 15 webkit 22 (unprefixed) |
6 webkit |
Backward playback using playbackRate < 0 |
? | ? | No support | No support | ? | ? |
Feature | Android | Chrome | Edge | Firefox Mobile (Gecko) | Firefox OS | IE Phone | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|---|
Basic support | No support | 28 webkit | (Yes) | 25 | 1.2 | No support | No support | 6 webkit |
Backward playback using playbackRate < 0 |
No support | ? | ? | No support | No support | No support | No support | ? |