Results

Well, the outcome is sort of what I expected.. Pretty much garbled video with no discernible shapes/objects.

I really would have liked to been able to swap out key frames but the amount of time to write such software would have been way too long for this project so I'll have to settle with random changes.

One thing I did notice is that when I manually changed things by hand there were some cases where you couldn't see ANY visible difference in the video. Either I changed dummy data (which is possible) or the MPEG2 error correction algorithms are pretty good.

They developed mathematical techniques used to predict values based on previous values in case the DVD is scratched and can't be correctly read. MPEG2 is the standard video file format for a DVD. It's pretty impressive how many changes you can make w/o changing the video.

Although 100 changes isn't much when we're talking about billions of bytes.. It's still impressive none the less.

It seems that after around 25% change the file just aborts playback after a second or so. I'm assuming this is because I've changed vital information about what image/keyframe to use next and overwrote it with garbage data.

This wouldn't be an issue if I could have wrote software to swap keyframes instead of just being forced to replace random parts of the file.