If you can get an Intel CPU, I think they are quite a bit faster at encoding/decoding video, even for the less powerful models.
Any recent i5-i7 or Ryzen 5-7 (i9 or Ryzen9 might be overkill)
A bit late, but for encoding/decoding video, GPU's are for years now (all DX11 cards minimal and higher) way more efficiënt (power consumption as video load) than a CPU. Each Chip-family has some hardware encoding/decoding codex build in and supported. CPU is not build for graphic-task, but is still able to process all types of them (only much slower and much more inefficient).