How to play multiple AudioBufferSourceNode synchronized?

Question

I have multiple audio files that must be played in sync. I have read that Web Audio API is the best solution for this. But, I can't find any document that shows how to achieve this.

Almost all articles I have read do this to start playback.

//Let's say I have AudioBufferSourceNode connected to two buffers
var source1, source2;

source1.start(0);
source2.start(0);

Shouldn't this cause source2 to start playing slightly later than source1?

Also, what makes the sources stay in sync? I can not find any mention in any documentation that assures that sources are played in sync.

Thanks.

Answer 1

You can schedule them slightly in the future.

var source1, source2;
var when = context.currentTime + 0.01;

source1.start(when);
source2.start(when);

That'll schedule both sounds to play exactly 10ms from the moment you define when. It's quick enough that it'll be perceived as immediate, but gives a bit of breathing room for the overhead of actually calling start on the first source node.

There are better ways to do this if you have a ton of nodes, but for simple situations, this should be fine.

Answer 2

There is a single clock for the audio context, and the buffer playback is on that clock - so yes, they will stay in sync.

Even calling start(0); start(0); as above will be perfectly synchronized, because start() is setting up a scheduling request on the audio thread, and the actual scheduling of both of those will happen together. "now" is actually slightly in the future (the audio system latency).