Nvenc_hevc - getting the best out of it

Useful and helpful Windows specific command line samples and examples.
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coremans
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Joined: Wed Oct 26, 2016 6:34 pm

Nvenc_hevc - getting the best out of it

Post by coremans » Wed Oct 26, 2016 7:21 pm

As it is very hard to get real documentation on the use of the Nvenc_hevc codec, I was wondering if someone has parameters to get the best out of it.
Source is Live UHD from a Decklink card and target is a TS over UDP. Card is a GTX1080

There is so little to be found, even the max bitrate is not available in any documentation, also missing is what each preset is exactly doing...

If any one can help or has experience ....

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UTAVATU
Posts: 5
Joined: Tue Feb 14, 2017 8:12 am
Location: Gdynia, Poland
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Re: Nvenc_hevc - getting the best out of it

Post by UTAVATU » Mon Feb 27, 2017 2:15 pm

Dear Friends

I would like to use encoder hevc_nvenc with my H.264 Blu-Ray movie collection and I have been searching for answers too and...

Variant A:

Code: Select all

ffmpeg -hide_banner -i input -c:v hevc_nvenc -preset hq -rc constqp -global_quality 21 -c:a libfdk_aac -ar:a 48000 -channel_layout:a 5.1 -ab:a 640k output
Variant B:

Code: Select all

ffmpeg -hide_banner -i input -c:v hevc_nvenc -preset hq -rc vbr -b:v 25000k -qmin 17 -qmax 21 -c:a libfdk_aac -ar:a 48000 -channel_layout:a 5.1 -ab:a 640k output
Values for lower then -qmin 16 (for example from 0-16) there is no visible quality loss on my Epson TW-5300 90" comparing to H.264 Blu-Ray. Sully - H.264 lossless with HD Audio also lossless is ~20GB with average bitrate 30500kbps, after using Variant B it's only ~5GB with average bitrate 7300kbps. Files are encoding with speed greater then ~7x-9x with my MSI GTX 1070 Gaming X8, so it's great advantage over libx265, where my Intel i5-4690K was encoding with speed ~0.9x-1.2x and I cannot see visual quality difference using:

Variant C:

Code: Select all

ffmpeg -hide_banner -i input -c:v libx265 -preset ultrafast -crf 12 -c:a libfdk_aac -ar:a 48000 -channel_layout:a 5.1 -ab:a 640k output
I would like to know, if -crf 12 used with libx265 is equal to global_quality 13 used with hevc_nvenc, where q=12?

Thank you in advance for any help and support.

Sincerely

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