The given list of FFmpeg and friends repositories are easily kept up to date with this one line bash script.
find . -maxdepth 1 -type d -exec sh -c '(cd {} && pwd && git pull && ./configure --help >> ../{}.configure.help.txt)' ';'
This could be used in a directory where the following repositories could have been checked. It will create several text files in the directory where is is run, that will contain help information for the specific configure options. The Git commands below are just for the sake of making them available as an easy copy-paste list once needed.
git clone git://source.ffmpeg.org/ffmpeg.git
git clone git://git.videolan.org/x264.git
git clone git://sox.git.sourceforge.net/gitroot/sox/sox
git clone git://github.com/Itseez/opencv.git
git clone git://anongit.freedesktop.org/pulseaudio/pulseaudio
git clone https://git.chromium.org/webm/libvpx.git
git clone git://git.code.sf.net/p/opencore-amr/code opencore-amr-code
git clone git://git.code.sf.net/p/opencore-amr/vo-aacenc
git clone git://git.code.sf.net/p/opencore-amr/vo-amrwbenc