Just updated to 2.70 from 2.6x (I think it was 2.65) and I seem to have the same issue in that my videos don't play anymore. (Win10 64bit, i7 930 CPU, Radeon 7800 displaying 2 monitors). Videos are f4v and encoded by pbxrecorder. I have the codecs.exe from this site installed. Everything was working fine, installed 2.70 over the old build (like I always do when updating) and videos are not playing now.
Will play around to see if I can get things going, can probably dig out logs etc if they help.