Replacing videos files in a PSP game?

[FlamePurge]

Hi everyone, I'm hoping you can help me out today.

I was hoping to replace the opening in the PSP port of Tales of Eternia with the original Japanese opening. For some reason, the North American version's (Which the European PSP version was based off of.) OP not only changed the music up, it rearranged and cut some clips from the video.

I tried simply replacing the video file with CD Mage, but it sadly didn't work--the end of the OP gets cut off and stutters. Does anyone have an idea on how I can go about this in a smarter way?

Before anyone suggests: I am not looking to make or get an undub! I know the undub exists, and I don't like it for the virtue of not being able to understand the map hints unless you press the Select Button. I just want the original OP in.

Thanks for your time; have a lovely day.

Edit - I've figured it out! I had to use UMDGen.