The Core i7 series has Hyper Threading (HT) which is useful for encoding videos and photos depending on if the programs (and video codec) supports HT. Games do not benefit from HT whatsoever. The decision to buy a Core i5 or the more expensive Core i7 (~$100 more) depends on how often you create videos.
AMD's FX CPUs (Bulldozer) can come in handy when creating / encoding video as long as the programs you use can take advantage of more than 4 cores. Assuming the same clockspeeds, Intel CPUs are more powerful than AMD CPUs (about 29% on average), so if the programs you use to create videos cannot take advantage of more than 4 cores, then there is no point in buying a FX CPU.
The vast majority of games only use 2 cores, a small fraction can use up to 4 cores. Therefore, most / half of the cores in a FX CPUs (FX-8120 , FX-8150) will just be idling and you will get a little less performance compared to an Ivy Bridge Intel CPU because of the above mention performance difference (assuming same clockspeeds).