How to divide the video into four parts at once?
ffmpeg -i coolpron.mp4 -filter_complex "[0:v]crop=iw/2:ih/2:0:0[tl];[0:v]crop=iw/2:ih/2:iw/2:0[tr]" -c:a copy -map [tl] -map 0:a -y 111.avi -map [tr] -map 0:a -c:a copy -y 222.avi


This produces 2 video files at same time, but you can add other parts.

But use it only if you have no other choice for your video wall. Better solution: write your own custom player.