okay i have mode you script a bit
im using ubuntu 19-04 x64
make a folder named splashscreens in $HOME/RetroPie and put all your videos in that folder
put this in you script
chmod 755 you script
this script plays a random video form this folder and load emulation station
the only isuse i have whit this is it show a little splash screen on top of video that emulation station is load-et, but it diapers ;)
#!/bin/bash
#hides the menubar and desktop
#gnome-terminal --full-screen --hide-menubar
#starts Retropie
gnome-terminal --full-screen --hide-menubar -- emulationstation &
#Plays video in VLC then exits. Replace quoted part with your video's location.
vlc --random --play-and-stop --play-and-exit --fullscreen --video-on-top --no-video-title-show "$HOME/RetroPie/splashscreens"
exit