A new unofficial firmware update for the Sony PSP game device is claimed to offer ability to plays mp4-AVC videos at a resolution of 480x272p.
Since its first release, Sony's popular PSP portable game machine has been treated by enthusiasts as an experimantal device. The PSP cracking scene continues with pace, following the recent news that the PSP can now play any PS1 game using the official emulator recently released by Sony, using a conversion utility. The latest modified firmware offers the device the ability to playback mp4-AVC videos at 480x272.
Note that what is patched refers to mp4 avc. Standard mp4 cannot play at resolutions higher than the multiplication of 320x240.
More information can be found here