compiling ffmpeg on OpenBSD

1) Install required packages like nasm, etc, following the CentOS guide below:
https://trac.ffmpeg.org/wiki/CompilationGuide/Centos

2) Install git, gmake, as well as x264, for H.264 encoding feature:
# pkg_add -v git gmake x264

3) check out the latest source:
$ git clone git://source.ffmpeg.org/ffmpeg.git ffmpeg

4) cd ffmpeg; ./configure --enable-gpl --enable-libx264 ; gmake .