Hardware accelerated transcoding
The computer must have Intel Core CPU with Intel HD Graphics 2000 or newer. That means 2nd generation and newer Intel Core CPUs are supported.
You can check if your CPU supports QuickSync here.
H.264 hardware decoding and encoding is supported on models with dedicated video encoder - these are models which also supports AirPlay Mirroring. Newer models also support hardware accelerated HEVC decoding.