Transcode UHD mkv to JUST < 50GB to fit on 50GB BDR-DL: Best app / settings to shrink mkv & (retain DV / HDR)?

[njweb]

Goal:
I want to burn backups of some of my original UHD Blu Ray movies on 50GB BD-R DL discs so I have a backup and play that in my Blu Ray player since many of my discs are limited editions / collectibles, out of print etc. and cannot be bought easily, if at all anymore.

Since I am burning to 50GB BD-R DL discs, I am not worried about maximum size reduction:
I just need the transcoded mkv to be BDMV/CERTIFICATE compliant so it plays in my Blu Ray player and fits on a 50GB disc, while maximizing quality, retaining Dolby Vision and HDR if possible and minimum transcoding time. It also needs to be compliant with the spec so that my Blu Ray player can play the disc.
(I tried makemkv full disc backup with one of my 1080P original disc and burned it to BD-R DL with ImgBurn and my Blu Ray player does play the discs, so I know it reads spec compliant BD-R's fine).
It seems most are backing up to HDD and want maximum file compression (while retaining quality), so I did not find any posts about my scenario where I just want to get the final mkv down to just under 50GB (e.g. 45 GB) to reduce transcoding time.

I am new to Handbrake. I tried transcoding one of my UHD Atmos movies which was originally 54.9GB (not a long movie) with Handbrake to reduce the mkv to under 50GB.
Video - I selected H264 (since it is faster than H265 and size is not a concern for me as noted above).
Audio - I selected TrueHD pass through (hope this is correct for Atmos).
Dimensions - It defaulted to 3840 X 1632.
The output of Handbrake transcoding came to 12.7 GB (only 1/4 of the capacity that my blanks can accommodate) and took ~5 hours.

So my questions are:
1. What are the highest quality / best transcode settings in Handbrake to reduce the original mkv file size just enough so the mkv fits on 50GB BD-R DL disc. This should reduce transcoding time significantly (due to less compression / less processing).

2. I read a post by Marty McNuts that Handbrake may not support Dolby Vision and HDR, so he uses TWO other tools instead of Handbrake (which adds another step and more time) to retain Dolby Vision and HDR.
Does Handbrake not support DV and HDR? I see the alternative mentioned is nvencc64 which (assuming my laptop's nVidia card is supported) requires a lengthy command line with all the parameters, along with TSRemuxer (which I would also use after Handbrake, but just to convert the final mkv file to BD-compliant ISO).

Any tips on best tools and settings to meet my objective of getting the UHD mkv to just under 50GB so it fits on a BD-R DL without taking so long to transcode would be greatly appreciated, thanks!
It needs to be compliant with the BD spec so it can play on my Blu Ray player.

[Woodstock]

Processing through handbrake is not your best option here, because you're going to lose your DV.

[njweb]

Processing through handbrake is not your best option here, because you're going to lose your DV.

Thanks, so that is definitely confirmed then. Appreciate it.
Come to think of it, luckily the majority of my UHD collection is not DV, so then I just need some guidance on the optimal Handbrake settings or other tool transcoding settings for minimal shrinkage and reduced processing time to get a 55GB - 70GB mkv down to just under 50GB for burning to BD-R DL (including any buffer so that the BDMV folder is still under 50GB) so it can play on my Blu Ray player.

[Woodstock]

The handbrake forum is the place to check for improving your settings. The standard advice, though, is to start with the presets, and move on from there if needed.

Keeping HDR is relatively new; you're going to have to work with their nightly builds to do it.

[njweb]

The handbrake forum is the place to check for improving your settings. The standard advice, though, is to start with the presets, and move on from there if needed.

Keeping HDR is relatively new; you're going to have to work with their nightly builds to do it.

Thanks, will do.


In the meantime, it appears TsMuxeR 2.6.12 sees my UHD mkv as an 'unsupported format' which surprised me. I created the mkv from my original UHD disc and it plays fine in VLC Media Player, as does the transcoded mkv. I converted it anyway and sure enough the .m2ts (in BDMV folder) does NOT play properly.

I got the same error in TsMuxerR whether I tried the original non-transcoded mkv or the transcoded shrunken mkv
I just want to convert the transcoded mkv into BDMV and CERTIFICATE folders so they can be burned to BD-R DL.
Edit - Think it was the way I selected the files to be converted to mkv perhaps.