There is a (quite demanding)
thread in the VideoHelp forum asking for a comprehensive official documentation of x264, similar to ReadTheDocs for x265. Does any exist which I missed? The VideoLAN homepage of x264 seems not to mention any, and the docs directory in the repo is hardly worth mentioning. So I guess the best source of knowledge appears to be the fullhelp combined with searching back in the developer mailinglist for discussions about every parameter...