Just to chip in...
If you are buying an intel CPU, then these all come with intel HD graphics. This will be more than enough to run videos at 720p.
AMD, however, only have integrated graphics in their A-series APU processors.
If you are to choose a processor which does not have some form of integrated graphics, then all you will need is the cheapest GPU you can buy. Like TechyInAZ says, a GT710 will be more than enough.