Custom firmware for portable MP4 players can be a game changer, especially if you want to unlock more features or improve performance. It's great for extending the life of older devices by adding support for new formats or improving the user interface. I tried to reformat mp4 to image sequence once, but it was because of this firmware (I think, though I could be wrong here) that it was just catastrophically difficult. Custom firmware can really extend the functionality of your MP4 player beyond the standard limitations.