How do you play mp4 files on your psp?

To play MP4 files on your PSP, first ensure the video is in a compatible format, typically H.264 or MPEG-4. Transfer the MP4 file to the PSP by connecting it to your computer via USB and placing the video in the "VIDEO" folder on the Memory Stick. Once transferred, disconnect the PSP and navigate to the Video section on the home menu to select and play the file.