PMF

PlayStation Portable Movie Format, abbreviated as either PSMF or PMF, is a video container developed by Sony Computer Entertainment and used in Persona 1 PSP and Persona 3 Portable. In the Persona games, the video track can be either MPEG1 or MPEG2 and is always 29.97 FPS. The audio track is always 48000 Hz stereo ADX. Most Persona 3 videos are 16:10 640x368 and get letterboxed in-engine. Some are made to display in 4:3 fullscreen, which use 640x448. All videos in Persona 4 are 4:3 640x448, except for its unused copy of the Persona 3 opening. They can be played outside of the game on MPV(found here), audio may glitch when skipping the video.

Modding
The length of the video files appears to be hardcoded into the executable. However, it is still possible to create custom video files equal in duration to the original.

PMFCreator
PMFCreator is an tool for creating PSP video files. To use it, you will need an MPS file, which can be created with UMD Stream Composer. Once your MPS file has been made, download PMF Creator with the link given to you.