gaming is all about memory bandwidth and feeding the vid card with data while doing lots of math to deal with game physics, these are things AMD processors are usually good at, games are also single threaded
video encoding is all about moving chunks of data thru the processor as fast as possible, but, the apps are usually small, so, with cache memory being speedier than system memory, cache size and raw clock speed if done right wins, and video encoding is easy to multithread or run a few in parallel so to speak