some mini updates: the videos I talked before (with no extension) are in .PMF format . Apparently, only Media Player Classic comes with the codec to reproduce it, but the codec doesn't reproduce the sound. If you want to play the files in your PC with another player you'd need the codec, and here it is:
http://depositfiles.org/files/hvkq5xbcz . There is something I think I didn't mention: I can play the video files, but the framerate is awful, it's very choppy.
No video editor recognise the .PMF files neither. What I'll try to do is to see if I can convert one cutscene to AVI, and if it keeps the framerate and gets sound, I'll edit it (change the sound), then convert it back to PMF and repack the CPK file again, and make a new ISO with that modified scene, and check out if it plays on my PSP or not.
update:
For the conversion I've found this awesome and simple program that converts the PMF to AVI and also extracts the AT3 file (that's why I didn't have sound). I'm glad that the AVI video is the same resolution as the original and has no framerate issues. Here's the program:
http://skybladecloud.wordpress.com/projects/psp-video-extractor-converter/
Now I'll see how can I do the audio replacement and compile everything again like I said above.
update 2:
I'm not 100% sure if this will work; the audio replacement is the most difficult part because someone would think "hey, why don't you just convert the english audio to at3, and combine it with the avi you extracted before into a new .pmf video?" but that can't be done (maybe the conversion to at3, using the psp with a special homebrew, but not the last part of combining everything).
So this is what I found: I have to have the extracted AVI, and the english audio should be with exactly this settings: the audio should be a .wav file with PCM format, 44.100 kHz, 16 Bit, Stereo 172kb/sec (I guess I'll have to see if Audacity can make that exact conversion). "Encode+multiplex" the two files using Sony UMD Tools and a there should be a new .mps file. And then convert the .mps with "mps to pmf converter" (this program was made for "gameboots" (I don't know what they are), so I don't know if it will work).
So yeah.... there are so many conversions and programs that I don't know if it will work
. I'm tired right now, I'll continue tomorrow or some other day (so far, I got to the part of the extracted AVI and at3 (useless for now) file)