Hi riccetts
Its not that hard to script this. But first, do you want the video to play on the "wall picture" as an overlay or full screen?
If you want an overlay on the "wall picture" itself BlackFox has posted excellent scripts just for this here..
http://forum.thegamecreators.com/?m=forum_view&t=192148&b=23&msg=2429889#m2429889
If you want full screen, use the "video=path" or "video=$0" action. I use the "video=$0" in my scripts as it seems easier.
:state=0:hudreset,hudx=50,hudy=90,hudimagefine=gamecore\text\pressentertouse.tga,hudname=pressenter,hudhide=1,hudmake=display,state=10
:state=10,plrdistwithin=60:hudshow=pressenter,hudfadeout=pressenter
:state=10,plrdistwithin=60,plrusingaction=1:video=$0,playfullvideo=1,state=11
:state=11:stopsound=0
Just attach your video to the entities "sound0" setting. In your case the "wall picture" sound0 setting.
The "state=11:stopsound=0" stops the video from looping.(plays once)
Hope this helps
best