H.264 Hardware Acceleration in Adobe Media Encoder - Good or Bad?
We have found that much of the quality issue with Hardware Accelerated encoding is due to it being limited to ~60mbps. If you try to set it higher than that (which the "H.264 High Quality 2160p 4K" preset does), Premiere Pro and Media Encoder don't follow the target bitrate and revert back to a very low bitrate. This explains both the low quality and faster performance found in our testing.
We plan to do a follow-up to this testing in the future.
Check out our workstations designed and optimized for Premiere Pro! https://goo.gl/vq37cX
Using Hardware Acceleration when exporting to H.264 in Adobe Media Encoder or Premiere Pro is supposed to dramatically improve export times. But we've found that there are a lot of odd things going on with bitrate and file sizes as well as a bit decrease in video quality with Hardware Acceleration enabled.