Avidemux Nvidia H264 / HEVC settings

[frenksisco]

I hope I will be able to explain this thing in spite of my bad English.
I know more or less the avidemux x264/x265 encoding settings but I'm little confused about the Nvidia H264 / HEVC encoding options.
Settings are very few but despite of this I don't find any documentation that explains the presets.
The preset are:
- Low Quality
- High Quality
- Bluray
- Low latency
- Low latency(LQ)
- Low latency(HQ)
- with the addition of Bitrate and Max Bitarate.
My question is: what does it mean High Quality specifically? What does it mean "Bluray" or the 3 "Low latency" options specifically? In standard x264 / x264 I can choose for example the "very slow" preset and the 18 constant rate factor to be pretty sure to use the maximum encoding quality ..... But here I see only adjectives...
So... In other words ... What are the Nvidia corresponding settings for "very slow" and "18 rate factor"?
Thanks!!

[LigH.de]

One reply for brief: The NVENC encoding chip will not reach the complexity of x264 or x265 in "--preset veryslow". It will certainly have a lower complexity. Especially the temporal scope will be shorter; hardware encoders will mainly rely on spatial compression, they are not made to search intensely for similarities between a lot of reference frames – but this is one of the main reasons of the advantage of good software encoders like x264/x265.

Now, what LQ or HQ means exactly, may even depend on the generation of the NVENC chip, thus on the graphic card model. Discovering that may require to analyze the result of your specific hardware. A "Blu-ray" and a "Low Latency" preset will only limit the encoding further, e.g. the number of consecutive B frames, the number of reference frames, the maximum length of GOPs (to at most 1 or 2 seconds, depending on the resolution, in Blu-ray compatibility case, and even shorter for Low Latency). Or brief: To be compatible to special hardware and usage demands, encoding efficiency will get worse.

Finally, a rate control mode based on a rate factor is available in x264/x265, but possibly not in NVENC encoder chips. Constant quantizer and a per-GOP average bitrate are more probable.

[frenksisco]

Thank you!