[kotxig]

You can compute an autocorrelation with FFT's by applying the convolution theorem which IIRC the audio api can do the FFTs for you. I also found the the YIN estimator is a lot better as a time domain estimator http://audition.ens.fr/adc/pdf/2002_JASA_YIN.pdf and some years ago I worked out how to compute that estimator with FFTs also.

[joren-]

For a Javascript YIN implementation, see https://github.com/peterkhayes/pitchfinder I have used it in a live spectrogram visualisation: https://0110.be/phd/presentation/spectrogram/live.html