How can I play audio in reverse with web audio API?

Question

How can I play audio in reverse with the web audio API? I can't seem to find anything in the API docs...

Answer 1

You could do something like this:

var context = new AudioContext(),
    request = new XMLHttpRequest();
request.open('GET', 'path/to/audio.mp3', true);
request.responseType = 'arraybuffer';
request.addEventListener('load', function(){
    context.decodeAudioData(request.response, function(buffer){
        var source = context.createBufferSource();
        Array.prototype.reverse.call( buffer.getChannelData(0) );
        Array.prototype.reverse.call( buffer.getChannelData(1) );
        source.buffer = buffer;
    });
});

It's a super simple example - but the point is basically that you can grab the Float32Array instance for each channel in the AudioBuffer and reverse them.

Answer 2

if you have an AudioBufferSourceNode element:

audioBufferSourceNode.playbackRate = -1;

-EDIT-

Webkit doesn't have that feature.

Source: https://bugs.webkit.org/show_bug.cgi?id=69725

Answer 3

You can use <audio> element of html5 and set playbackRate property to negative value.

In Javascript you can do the following

var song = document.getElementsByTagName('audio')[0]; 
song.playbackRate = -1; 

Answer 4

playbackRate = -1.0;

works in Safari (9.1.2) now!