Slow transcode speed from HEVC 10-bit source, but also low CPU

[vlix 1]

Hi!

 

When I let Emby transcode a UHD Blu-ray source (untouched .m2ts file), performance is very bad (~17fps), causing constant hiccups during the streaming. However:

 

1) My Emby Server has a Ryzen 1700 8-core processor, which should be adequate to do a 1080p 24fps encode at higher than realtime speed

2) I`m using my video card (Geforce GT1030) to offload the decoding of the HEVC source, so that's not hogging the CPU

3) CPU utilization is only 20% or so, and only 4 cores are used at all, even when I configure Emby Server explicitly to use 8 cores for transcoding

 

Transcoding standard, non UHD Blu-rays (from untouched AVC .m2ts source) works fine, at 90-100fps. CPU utilization is at around 30%, which still seems low.

 

Throttling is not enabled, H264 encoding preset is "superfast" . I have included a logfile (slightly redacted for private details)

 

I hope someone has an idea what's going wrong here... thanks very much!!

ffmpeg-transcode-c04f8808-7f66-419f-a24f-1ca97860d095_1.txt

[ebr 16187]

1) My Emby Server has a Ryzen 1700 8-core processor, which should be adequate to do a 1080p 24fps encode at higher than realtime speed

 

Hi.  Upon what are you basing that assumption?  HEVC 10 is an extremely challenging codec and you are also burning in subs at the same time.  Does it improve if you deselect the subtitles?  Have you played with any of the hardware acceleration options?

[vlix 1]

Hi.  Upon what are you basing that assumption?  HEVC 10 is an extremely challenging codec and you are also burning in subs at the same time.  Does it improve if you deselect the subtitles?  Have you played with any of the hardware acceleration options?

Hi ebr, thanks for answering. Unless my understanding is wrong, HEVC is only involved in the DEcoding phase, and that is being taken care of by the GPU. The ENcoding is being done in AVC/x264. My GPU is not capable of hardware ENcoding so I have to do that in software, but it`s my assumption that that should not be much harder than encoding from an AVC source (ie regular Blu-ray). Is that assumption wrong?

 

- I have tried both NVDEC and DX11VA for decoding, it doesn't make much difference.

 

- I have tested DEcode hardware acceleration by playing back the same file in VLC, with hardware acceleration. This works absolutely fine.

 

- Deselecting subtitles does indeed improve performance, but only a little: ~27fps, still nowhere near the 100fps I get with regular Blu-ray transcoding.

Edited January 8, 2020 by vlix