It's easy to roll your own ffmpeg/mplayer for OS X (use macports if you want it really easy). What's not so easy is to make a statically build version (with statically build dependencies) which is redistributable and works on Tiger (could maybe be dropped now), Leopard and Snow Leopard, which is basically what is required for PMS inclusion. I made the build currently in PMS so it can be done but it's a pain in the ass and I've since lost all the configs I had for it. The build otmanix made for instance will only work on the mac that it was build for (well, once you add configure options at least), because by default everything is built against dynamic libraries and only for the current OS. There is lots of info in the original OS X issue (
http://code.google.com/p/ps3mediaserver ... etail?id=6 , especially my comment 105) on what's needed, however the main resource on that page (a wiki on how to build it all) has since gone offline unfortunately.
It's best to use the same dependencies as the sherpya builds (at the bottom of
http://oss.netfarm.it/mplayer-win32.php you can find the configure) since those builds are used by PMS on Windows.
For mencoder-mt you can just build like normal but replace the folders libavcodec, libavformat, libavutil with the version from this repository:
http://gitorious.org/ffmpeg/ffmpeg-mt