I would like to use libavcodec
for a project, the problem is i don't understand where i'm supposed to get the official release, this library is so popular that i can't tell what is the official website.
for example there are 2 major projects like libav and ffmpeg that are using it but i can't find the official source.
Where is this website ?
The official site is at ffmpeg.org. You can get the source with git or by using a release tarball. Git is recommended as it will provide the most up-to-date code and is stable the vast majority of times (and fixes come quickly). The release tarballs were designed for distros who "need" a release. See the FFmpeg download page for more details.