For some reason, my 3.1.2 JB iPhone stopped playing video correctly. When I play any type of video - Youtube, my own video, a movie, anything, the screen goes blank -- even though I can still hear the audio.

It's like the codec for the video got corrupted somehow.

Is there any way (perhaps through an iPhone Explorer program) to reinstall the proper codecs to get my video working again?

I read on some post that the person had to restore their phone, but hoping I can avoid that by replacing the proper file back where it should be.