@sphirst You can accomplish this by editing your runcommand-onstart.sh script, as @herb_fargus mentioned.

edit /opt/retropie/configs/all/runcommand-onstart.sh nano /opt/retropie/configs/all/runcommand-onstart.sh then paste the following into script (it checks if the system is psx, if so, play the mp4): [[ $1 == *psx* ]] && omxplayer -o both -b --layer 10001 /path/to/your/ps1.mp4 lastly, which I'm not sure is even necessarily, but make it executable. chmod a+x /opt/retropie/configs/all/runcommand-onstart.sh

In case you need it, here is the ps1 boot screen (mp4 format): https://dl.dropboxusercontent.com/u/23611685/video/ps1.mp4?dl=1

@Hex thanks! Very cool cardboard Gameboy!