Playing and Recording with a constant latency on browser with javascript usermedia and web audio api

Question

My application play a music using web audio api with MIDI.js.

Application record a user from microphone or webcam playing an instrument like guitar. I am using getUserMedia with a worker for this taken from https://github.com/mattdiamond/Recorderjs.

My problem is a latency problem. The sound I played is approximately recorded 250ms after.

What I want is not necessarly to reduce this time but to know this time with more or less 15ms so I can synchronize both.

Is there anyway to do it ? Can I assume the latency will stay constant ?

I noticed the AudioContext parameter call currentTime: http://www.w3.org/TR/webaudio/#AudioContext-section Can I use it to know the latency between my noteOn and the realTime noteOn on hardware ? If yes then how and how can i get the latency between guitar playing and guitar recorded.

I need something like AudioIODevice::getOutputLatencyInSamples from JUCE http://www.juce.com/api/classAudioIODevice.html#a693804fbf5a7cceb31ece10a9f03bd11

Thank you for your help.

Answer 1

Right now, there's no way to do this; the currentTime exposed is audio hardware time, and there's no direct conversion. We have an open issue to add it to the spec.