Great article. I just cannot contain my need to nitpick (I have background in Ultrasound signal processing). It's Hann window. Not Hanning window. There is a w

Great article. I just cannot contain my need to nitpick (I have background in Ultrasound signal processing). It's Hann window. Not Hanning window. There is a window function called Hamming window due to which some mistakenly add the 'ing' to Hann window too. Second of all "In summary, with a 6-second window, we get a tolerable 6-second startup delay that gives a fair time accuracy of 6 seconds and a fair frequency accuracy of 5 bpm (half the FFT resolution)" is bit incorrect. You do get far more accuracy in determining the frequency of that single signal. What the window length determines is the limit where you can separate 2 signals. So using that window you would mix up 2 signals that are 5bpm or closer to eachother and they would look like a single signal. Having 2 humans with similar heart rates in same video stream would thus be unseparable using that length. But you can determine the heart rate of a single individual with far more accuracy. The correct term would be "precision" as per http://en.wikipedia.org/wiki/File:Accuracy_and_precision.svg http://en.wikipedia.org/wiki/File:Accuracy_and_precision.svg Nonetheless this is an excellent article.