You setup a powerpoint presentation on your normal work machine, the encodes you did in mp4 worked just fine in the presentation. Save out to a stick and take it to the machine (an all in one touch screen 65″ with powerpoint viewer only) and all you see is a black screen where your video should be.
Scoured the interweb and tried three different encoding solutions, all of which resulted in a black screen.
I then upgraded the powerpoint viewer on the display machine from 2007 to 2010 (or the latest one I could find on the Microsoft pages). Bingo, the video started working.
Here is the encode I used which worked best, allowing proper full screen video, no black bars, etc.
ffmpeg -i input.mpg -q:v 4 -c:v wmv2 -c:a wmav2 -b:a 128k output.avi