I'm guessing that it's details on the encoding of said videos. I imagine the "audio stream" portion is the only thing relevant. I wouldn't think that it would be AC3 that is the problem, as isn't it a pretty common audio encoding for videos these days? Beyond that, the rest of it could be a foreign language and I would understand it about as well. Honestly not too up on video standards and the like. If need be, I can provide a link to a video that this occurs on.Stream count: 2
1: video stream, V_MPEG4/ISO/AVC, 1280x720, display: 1280x720, 29.970 fps
2: audio stream, A_AC3, 2 ch., 48000.000 Hz
Note that the videos in question play perfectly fine with VLC. Though MM does do better than WMP, as it doesn't seem to like MKVs at all.