Problems converting 4K HEVC HDR-10bit videos to 4K SDR H.264

[Emy78]

Hello everyone.
I've been a long time Videohelp lurker, and finally I decided to join this wonderful and very informative forum to show my support to the community, as well, maybe, give some help to people in regards to audio/video conversions.
I've been a long-time audio-video editor, and I hope that my knowledge can be of help to someone here.

Anyways, as the title suggested, I'm having a very hard time with 4K HDR-10bits videos, as of lately.
I've been getting into 4K Blu-Ray recently, bought some titles as well a UHD-friendly drive to use with my PC. However, as with all new things (audio-video related), there's always some trouble getting things working right.
Many years ago I've been on the same boat with DVD-Audio, Super Audio CDs as well some DVDs/Blu-Rays and lossless audio as well.
Edit audio-video as a job is a thing. Converting/fixing things is a total different story. And thanks to this as well another forum, I managed to get most of my problems solved.
However, this time, I seem to have some real troubles getting what I need, which is essentially converting 4K HDR HEVC videos (.m2ts, .mkv) to 4K SDR ones (possibly in H.264).
My computer is pretty old, but still does play 4K SDR videos in 10-bits just fine, VR videos from Youtube as well 3D Blu-Rays just fine. Even demanding games like GTA V and Flight Simulation software plays fine. It's only 4K HDR/HEVC that's giving me the nerves.
So far I tried DVDFab, Handbrake, Xmedia Recode and FFMPEGYag without success. And none of these encoders seem to use the NVIDIA 540m GT GPU that I have at all......only the CPU gets used. But a 1hr movie takes nearly 9 hours to convert and won't convert more than just 30 secs, as the frames after 10 minutes seem to just go down to 0.
Playing the videos, as is, is a stutter mess. But I'm on Windows 7. And Windows 7, according to some users, can't software-decode 4K HDR videos as 10 does.
I read that Windows 10 HEVC component will play 4K HDR videos even on older hardware with madVR just fine. I still haven't updated to Windows 10, yet. So I'm not quite sure about that.
But, suffice to say that I'm not enjoying this 4K thing at all, for now.
I really wanted to convert some 4K movies to SDR to watch them on my non-HDR screen, but I'm definitely stuck at this point.
If someone can suggest me a software, or how I can force an encoder to use the GPU, so the conversion won't take a day to complete, it will be awesome.

Thank you.

[Atak_Snajpera]

..

[Atak_Snajpera]

You have extremely outdated GPU (fermi) from 2010. It does not support hardware encoding . I'm surprised that you didn't event bother to check than in google.

[Emy78]

I know that.
But, there must be a way to convert these videos or not?
Any program that will convert these without any issues?

[Emy78]

You have extremely outdated GPU (fermi) from 2010. It does not support hardware encoding . I'm surprised that you didn't event bother to check than in google.

Also, how come some people with older GPUs than mine, like ATI Radeons pre-HD series managed to play/convert these files just fine, and I seem to not be able to do that?!
Do ATI cards have special drivers or NVIDIA simply doesn't get anything right? I wonder.
Besides, 4K videos shouldn't be that taxing, compared to 4K gaming, VR and 3D.
Like I said, 4K SDR videos (even 10-bits ones) play just fine on my machine. It's just those with HDR that are a bugger.

[Atak_Snajpera]

What are you taking about? Even Radeon HD 4850 did not have hardware encoder! Is that hard to check specs on Internet?
https://en.m.wikipedia.org/wiki/Video_Coding_Engine
https://developer.nvidia.com/video-encode-and-decode-gpu-support-matrix-new#collapseOne

[Emy78]

What are you taking about? Even Radeon HD 4850 did not have hardware encoder! Is that hard to check specs on Internet?
https://en.m.wikipedia.org/wiki/Video_Coding_Engine
https://developer.nvidia.com/video-encode-and-decode-gpu-support-matrix-new#collapseOne

No, it's not hard.
And I already checked my card specifications many months ago.
What I'm looking is a program that will allow me to convert from 4K HDR to 4K SDR without any problems.

[davexnet]

There's some info in this thread
https://forum.videohelp.com/threads/399320-Converting-BT-2020-down-to-BT-709

[Emy78]

There's some info in this thread
https://forum.videohelp.com/threads/399320-Converting-BT-2020-down-to-BT-709

This is exactly what I was looking for
Many thanks for this.
I'm very familiar with both AviSynth and VirtualDub, so that should definitely be a walk in the park. Though I might need some help with the correct lines to use in the script.
Thanks again for this.