I think it was just a .wmv if I remember correctly...point is I sent that to all my PC users and she was the only one who couldn't open it on a Mac even though an employee of an Apple store...
Then your ex-wife is ignorant... or you are not telling the truth. Macs can easily play WMVs with the installation of Microsoft's own Flip4Mac. However, MS has refused to make its latest WMV11 available and has not released the codec for that format for any other platform... so It could be that Digital Rights Format file was what was not playable... but that is a special case...