The overriding answer is simple: AVC in Vegas doesn't support Hi10p422 profile or HDR. Never was a format, really, because HEVC spec was already in use.

Besides a compatible source and parameters, you need a compatible encoder, and there are only a couple!

I can't answer your question about screen compatibility.

However you aren't using the Leeming LUT right as it only works to transform HLG 3 to Rec 709 and requires a Rec 709 timeline. Paul hasn't yet completed any HDR profiles or documented the needed workflow.

Thank you Roger, lots of new stuff to learn. I was under the impression that the Rec.709 specification was intended for HD footage, and Rec. 2020 was for UHD and HDR, but I'll spend a bit more time reading.

The overriding answer is simple: AVC in Vegas doesn't support Hi10p422 profile or HDR. Never was a format, really, because HEVC spec was already in use.

Besides a compatible source and parameters, you need a compatible encoder, and there are only a couple!

Thank you, but that's a bit confusing/disappointing. Are you saying that while Vegas supports HDR in the edit workflow, when it comes to the final step it can't render HDR? That seems counter to what the Vegas page all about colour grading HDR ends up with:

https://www.vegascreativesoftware.com/us/video-editing/hdr-color-grading-in-post-production/

If that's not the case, then do you have any experience with compatible encoders?

I'm interested with HDR editing. I'm currently using BenQ PD2700U 4K monitor

https://www.benq.com/en-us/monitor/designer/pd2700u.html

Which says it can display HDR10, during the video editing process. Does this means I need to activate this HDR "switch" every time I wanna preview HDR content?

Also, only HLG footage/HDR media can be used in HDR workflow right? its a physical LOG data that can display true HDR right? U wont get HDR video from Slog/REC709?

Vegas supports hdr rendering for both AVC and HEVC.

Only HDR10 preview is currently available, as no gpu's natively output HLG (nor does windows).

HDR tvs work just fine for hdr preview in Vegas, assuming they are connected to a hdr compatible gpu and windows has been set to hdr mode on that monitor.

HEVC is the preferred output method as far as compatibility goes for HDR output.

This isn't true, you can render to h264 in 10 bit HDR in VEGAS, however it won't play in many players.

I stand corrected, red herrings and all. I wonder why they even included this in 18, it's a dead duck?

It's been in since 16... but yeah, use HEVC.

I can't answer your question about screen compatibility.

However you aren't using the Leeming LUT right as it only works to transform HLG 3 to Rec 709 and requires a Rec 709 timeline. Paul hasn't yet completed any HDR profiles or documented the needed workflow.

Thank you Roger, lots of new stuff to learn. I was under the impression that the Rec.709 specification was intended for HD footage, and Rec. 2020 was for UHD and HDR, but I'll spend a bit more time reading.

No, there is no difference between 4K and HD- both are Rec. 709 generally. Rec 2020 is for HDR. Leeming LUT lets you capture colors in the wider Rec 2020 space for HLG but then remaps the primaries for use in a Rec 709 timeline. FWIW I was a beta tester for Pro II on Sony.

REC 709 is also included as a subset of REC 2020 spec.

HEVC is the preferred output method as far as compatibility goes for HDR output.

Thank you for the accurate information and for the suggestion. I've rendered in HEVC and still none of the Sony displays recognise the file, not even a preview or duration is displayed. I was hoping to render to a file and then view it locally by way of a review process, rather than having to upload to YouTube and use it as a test platform.

No, there is no difference between 4K and HD- both are Rec. 709 generally. Rec 2020 is for HDR. Leeming LUT lets you capture colors in the wider Rec 2020 space for HLG but then remaps the primaries for use in a Rec 709 timeline. FWIW I was a beta tester for Pro II on Sony.

Thank you @RogerS - that makes more sense now.

HEVC is the preferred output method as far as compatibility goes for HDR output.

Thank you for the accurate information and for the suggestion. I've rendered in HEVC and still none of the Sony displays recognise the file, not even a preview or duration is displayed. I was hoping to render to a file and then view it locally by way of a review process, rather than having to upload to YouTube and use it as a test platform.

Hook the TV up to your PC via HDMI directly out of your graphics card. Assuming your card is HDR capable (all cards made in the past couple years are), go into windows display settings (by right clicking on an area of your desktop with no shortcut icons, assuming you have windows 10) and turn HDR mode on (make sure you have the correct display selected, or you may not see that option). Now your TV will be showing a HDR preview directly. Now you can watch your HDR videos on the TV without having to upload to youtube, and you can also preview your video in HDR as you are editing it, assuming you have VEGAS' project properties set to HDR10 mode (HLG cannot yet be previewed in Windows). HLG can be converted to HDR10 easily, by the way.