After I did some serious testing last night, I've discovered that the best plan (
to avoid messing up DVD playback) would be to download and install the CCCP (Combined Community Codec Pack) rather than downloading FFDSHOW on it's own, unless you're really brave and want to use one of the bleeding-edge builds of FFDSHOW.
You can download CCCP here:
http://www.cccp-project.net/I strongly recommend that you
read the install FAQ and follow the instructions on running CCCP Insurgent and removing any pre-existing CODEC packs you might have previously had installed, as they can sometimes cause conflicts and problems. This would include especially: previous versions of FFDSHOW, DirectVobSub, AC3Filter, and any of the other popular "codec packs" out there like K-Lite Codec pack.
After installing CCCP you may need to also enable the DirectShow option for mp4 media in MC... In MC, go here:
Tools --> Options --> Playback --> DirectShow Options and enable the checkbox.