webcam libav

I tried to read from a webcam using the libav library or the ffmpeg equivalent, which are obviously not well documented w.r.t. this specific matter. I realized that the following call is required at the beginning of the program :

avdevice_register_all();

not to mention
av_register_all();

To install  ffmpeg and the corresponding original libraries  on Mint, the following tutorial works well:
http://trac.ffmpeg.org/wiki/UbuntuCompilationGuide

A working code example
https://github.com/j0sh/thesis/blob/master/capture.c