i dont know if u know this, but i read in shea silvermans blog a way to put an intro video in piMAME. i try the same way with retropie, and it works!!!
yes, thats the link. thank you for post it. maybe a new section in the forum for videos??? XD. as i can see, the videos must be 26 or 27 seconds long to finish when retropie is totally loaded (at least in my pi)