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I find Microsoft Windows Vista Media Center is great in so many ways, but nothing's perfect (more's the pity).

One thing which has been irritating me for a while is how it was using the "shrink-to-fit" method of sizing local video playback instead of "expand-to-fit". This results in any wide-screen videos losing the left and right edges, as I only have a 4:3 monitor (shame on me). I believe it'd be causing equal problems with non-wide-screen videos if I had a wide-screen monitor, though.

Until a few days ago, I'd been using ffdshow's capable suite of options to force output into 4:3 (while preserving the aspect ratio, i.e. adding evil black bars). This really eats CPU, even on the fastest resize mode, increasing usage by approximately 30%, which was actually causing my AMD64 3200+ (2.0GHz) to run out of cycles on some videos.

What I found a few days ago, though, was the real solution: time to start the Registry Editor, folks. Locate the following key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\VideoSettings

Under this key there are a large set of options, most of which you don't want to touch. In this case, however, one particular one is crucial - ZoomMode_Video. Set that to "0". Done.

Footnote: There are 3 other ZoomMode_ options (ATSC, DVD, TV) and all 3 were already set to "0" here. ZoomMode_Video, however, was set to "1". I'd be very interested to hear how many, if any, other people have any of these ZoomMode_ options not set to "0" and which ones.

I have a Matroska (.mkv) file with the following tracks (data streams):

Tracks : 2
Track 1 : Video
   - Codec : (V_MPEG4/ISO/AVC)
Track 2 : Audio
   - Codec : MPEG Audio 1, 2, 2.5 Layer III (A_MPEG/L3)

Nothing particularly special there; I have the following relevant DirectX Media Objects (DMOs), DirectShow and Media Foundation codecs installed:

• Haali Media Splitter: a DirectShow splitter filter for Matroska files, among other container formats (analogous to the AVI Splitter for .avi and others).
• ffdshow: a DirectShow decoder filter for just about anything, including MPEG-4 Video and MPEG-1 Audio Layer 3 (MP3).
• Windows 7's in-box DMOs decoder filters for MPEG-4 Video and MP3. These can be used by both DirectShow and Media Foundation.

Question: What happens if this Matroska file is played in Windows Media Player or Windows Media Center?

Answer: No video and audio stutters a lot.

Question: Why?

Answer: Both will try to use Media Foundation first and DirectShow second. As Media Foundation has no preferred splitter for Matroska files (either in-box or that I've installed), it hunts for a supported transform (similar to DirectShow's filters) with which to play the file; the MP3 transform duly indicates that it can play the file.

I believe this is because the MP3 decoder ignores the data at the start of the file which it doesn't understand (to allow for ID3 tags) and then picks up the first frame of the audio stream inside the file. The stuttering is most likely it attempting to play back the video frames of data (the two data streams are interleaved within the container).

The solution: Amazingly simple; the only thing that matters is that they're trying to use Media Foundation first, so set one registry key to indicate .mkv files prefer to be handled by DirectShow and it works great in both players.

HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer\Player\Extensions\.mkv
    Runtime    REG_DWORD    0x7

Done.