Nintendo has just updated the Play-Yan page with a ZIP file download, containing a 544KB firmware patch for the Play-Yan media player. The update allows the Play-Yan to playback MP4 movies in high-quality stereo sound. After unzipping the patch, the file must be placed on the same SD card that contains the MP4 movies, and then they will be displayed on the movie menu as normal.
The page with the update also contains a small preview clip showing off the higher quality movie format. The clip is of the Link and Sheik extra movies from Super Smash Bros. Melee, and they look amazing on the small screen of the GBA or DS. They sound even better thanks to the substansial boost in audio quality that the update brings to the table.
Although the patch allows the playback of the MP4 format, there is currently no official Nintendo software that can encode into the format. The Media Stage software that comes with the Play-Yan doesn't, but an update is coming for that program next month. In the meanwhile, reports from around the Internet say that MP4 encoders for the Sony PSP, such as PSP Video 9, work just fine for converting files to the Play-Yan, as both can now use the same MP4 format.
