Just to add a bit here and to offer my $0.02 or less , HEVC encoding does use quite a bit more resources and really heavily depends on the CRF/VBR settings used and the encoding preset. I did a lot of research on this and the claim that a CRF of 23 when encoding a Blu-Ray source is visually lossless is just not true. If you have a good display, like a 4k with a larger screen, you can certainly see the difference.
I ended up going with CRF 12 to get to visually lossless with my setup when encoding my collection to HEVC. CRF 23 with the Ultra Fast preset does encode pretty quickly, but you can see the difference between source and destination material. This is fine for smaller devices, but any larger device that can handle the output will suffer in quality with transcoding. For those with hardware accelerated HEVC support, there won't be much of an issue until the transcode tries to output at a 4k resolution because the device is 4k. The output resolution would need to match the source.
Also, some source material encodes much faster than others, depending on CODEC, picture quality, motion, etc. VC-1 for instance normally went at about 15 FPS (some lower and some higher) on my server with 2x E5-2660 Xeons. The 32 logical cores struggled greatly without hardware encoding support. Those titles take nearly twice as long as the source video length to transcode with output being 1920x1080. Titles with HEVC typically ran at about 28 FPS but still very CPU intensive and it would never be able to encode fast enough to handle 2 encodes at once if it were on-the-fly.
HEVC is great for reducing the size of your video library, even though at CRF 12 some few files end up being larger than the source. Even at that CRF, the overall size of my library was reduced by slightly more than 50%. However for on-the-fly transcoding, this would not be a viable option for me without some significant hardware assistance.
Edited by otispresley, 03 August 2017 - 06:44 PM.