Yep, I went through all that and none of the common codec packs helped (I installed many of them). The Matroska Video file (.mkv) rendered audio once I'd installed DirectX9, but the video was impossible until I'd installed Realvideo 6. I tried the codec (after finding out what a drv4 codec was courtesy of http://www.mplayerhq.hu/homepage/codecs-status.html) alone, but it wouldn't take until I did the full boat install. I have to say that the corporate version of Real's product (soul-sucking registration required) is not at all obnoxious - no ads nothing (screenshot attached).

One side benefit of mass codec installs is that pretty much anything plays on my machine now!

-Zeke