Instructions
Download GSpot to troubleshoot your videos codecs. A codec codes and decodes video, and the PS3 can only read certain kinds of codecs. Click "File", then "Open". Select your video and compare the codec with the ones supported by the PS3.
Open a PS3 video converter like PS3 Video 9 or PS3 Video Converter. Click the "Add" or "Browse" buttons, depending on your program of choice, and select your MP4 file. Click the "Convert" button and create a PS3 compatible video.
Open your video file using the Playstation 3's XMB (Cross Media Bar) menu.