H264 encoded videos won't play on OS X 10.8

Hi. I used to always select H264 as my preferred video output codec, because it allows me to set the exact bitrate I want it to use.

However, that was on OS X 10.5 and 10.6, but I recently acquired a new machine, running OS X 10.8, and now whenever I export a video, my system doesn’t want to recognise the video format anymore.

I know I can export using Quicktime codec and then selecting H264, but that doesn’t let me enter a bitrate, there’s just a quality slider that results in files that are 2x larger than the source material, even at 50% screen size.

How can I get my system to just play the files as it’s supposed to? I tried downloading ffmpeg and h264 codec things, but it’s not helping.