MythTV can forget how to decode mpegs

Today I was surprised to find that my mythbox was unable to play back any of my recorded programs, including some of which I had watched as recently as yesterday!

By starting mythfrontend from a konsole, I was able to see an error message like:

NVP: Couldn't find a matching decoder for: [path to mpeg file].

Hmm, really? MythTV can't decode an mpeg file?

After some surprisingly futile googling, I eventually hit on the explanation: Last night, I had instructed my mythbox to record a movie on some channel that I apparently don't actually get. So the video file for this recording was somehow corrupt. Ok, so how would that cause mythtv to be unable to play the rest of my recordings? Is the corruption contagious? No, I think the answer is in the thumbnail preview shown for the selected video in the list of recordings. Since the invalid video was the first in the list, mythtv always tried to show its preview. Somehow, the decoder found this file so distasteful, that it refused to chew on any of my other mpeg files!

Anyway, I deleted the offending recording: problem solved. Since it would be nice if MythTV didn't choke up like this when given a corrupt video file, I filed a bug report describing the problem.