## An ffmpeg and SDL TutorialPrintable version Text versionThe function we are using is a weighted mean using a geometric series as itsweights. A weighted mean is defined like this:             w_0*x_0 + w_1*x_1 + ... + w_n*x_n    ---------------------------------         w_0 + w_1 + ... + w_n    If you substitute 1 in for each w_n, you get your normal everyday arithmeticmean (a.k.a. an _average_). Our function is basically a repetition of:             total = d_x + c*avg;    However, you can also look at it like this:             total = c^n*d_0 + c^(n-1)*d_1 + ... + c*d_(n-1) + d_n    in which case, this is just the top part of a weighted mean with c^n,c^(n-1)... as the weights. That means the bottom half is c^n+c^(n-1)...,which, as you may have guessed, is a simple geometric sum which works out to1/(1-c) as n approaches infinity. So, by approximation, the weighted mean of our sequence of diffs is simply:              total         -------  = total * (1-c)       1             -----     (1-c)    So when we get the final total and want to know the average, we just multiplyit by 1-c and get the answer! There is probably a name for this way of takingthe mean of a sequence, but I'm pretty ignorant and I don't know it. If youknow it, please email me. * * *Function Reference  Data Referenceemail:dranger at gmail dot comThis work is licensed under the Creative Commons Attribution-Share Alike 2.5License. To view a copy of this license, visithttp://creativecommons.org/licenses/by-sa/2.5/ or send a letter to CreativeCommons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.    Code examples are based off of FFplay, Copyright (c) 2003 Fabrice Bellard, anda tutorial by Martin Bohme.