So I downloaded a bittorrent of Waters of Mars. That was a new thing for me, but it seemed to go well (and I'm pleased with the speed of my connection). I have a large .mkv file sitting neatly on my hard drive.
I am running Mac OS X 10.4.11, with a 1.7 Gigahertz processor; the version of the VLC player I can support is 0.9.10 (not the latest one). The audio track plays beautifully, but the video track gave me only a black screen at first. I've now gotten it to give me random pixelated frames along with the audio. This was achieved by pushing cache latency as high as I can, including a manual setting recommended by someone on a support forum; I've also turned off the "skip frames" preference, but that seems to make no difference either way.
It's tantalizing, to hear the first minute of audio over and over, but only with ugly flashes of video. I want my Doctor!