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.
Video Summary
In the update notes for Media Encoder and Premiere Pro CC 2018, Adobe has listed support for “hardware accelerated” when exporting to H.264 and H.265 when exporting. What this feature does is to utilize the Quicksync functionality built into some Intel CPUs in order to dramatically decrease the time it takes to export to these codecs. At first glace, this feature provides a huge boost in performance for many users, but unfortunately it is not perfect.
The first issue is that it requires a CPU that supports Quicksync and you also have to make sure the onboard graphics on your motherboard is enabled. You do not need to have a monitor plugged into the onboard graphics, it just needs to be on so that Quicksync can be active. The problem is that most of the best CPUs for Premiere Pro and Media Encoder (the Intel X-series) do not support Quicksync so many high-end professionals simply won’t be able to take advantage of it.
The second issue with hardware accelerated encoding is that it is not the same quality as using the normal “Software only” mode. In fact, in our testing we found that the target bitrate was not always being met when using hardware acceleration. And even when it was, the quality was still lower than “Software only” mode. The odd thing was that when the bitrate was being matched, the time to export was identical in both modes – so we only saw a performance gain when the final exported file was at a lower actual bitrate.
If you are simply looking for the fastest encoding times (proxy generation, etc.) of H.264/H.265, hardware acceleration is a pretty neat and useful feature. If quality is a concern, however, it may not be worth the loss in quality unless you are on a tight deadline.
H.264 Match Source – High Bitrate
H.264 High Quality 2160p 4K
Software Only
58 Sec export – 183.4MB exported file
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Hardware Accelerated
31 Sec export – 34.4MB exported file
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