If your timeline preview will not handle it, make a proxy.

 

Well I think it helped. At least for now. Hmm never knew about this feature god damn. You probably helped not only me but a lot of people I know.. :))

Still seems strange that when starting vegas it glitches youtube videos and forces them to lowest quality.. but well.. that is not a problem I care about now.. It does not affect workflow. ;))
THANK YOU.

Just for your information, a lot of people have had issues in most all of the NLE's with the HEVC codec that GoPro used. Not only what you have with the Hero 7, but also those of us that have the Hero 6 Black and do the 4K60, as it is in HEVC as well. The only thing from GoPro's Support site that I have been able to find concerning this, is actually "re-wrapping" the footage into an .mp4 container using HandBrake. Though, others here would advise against that since you are doing another "compression" of the footage.

I tried taking a sample from my Hero 6 Black at 4K60, bring it into Sony Catalyst Browse (at least it's free), and Transcoding into XAVC-I, which would it in an .MXF wrapper. Didn't work a few months back for me though in Vegas Pro 15 or Movie Studio Platinum 15, though I know there has been some updates to Catalyst since. With only having Davinci Resolve 15 Basic (the free version), since it was 4K60 it would not read it at the time correctly either to Transcode to DNxHR file, again prior to the current 15.2.2 build (I was using an at the time earlier 15.1 something build), so again posssibility.

If you can at least put one clip on the timeline, and do nothing else to the file - no fx, color grade/correction, titles, anything, you might be able to just open up the "Render As", and try either the Magix Intermediate, or what I prefer is the QuickTime 7 DNxHR.

I believe if you go to the Movie Studio Zen website (MovieStudioZen.com), Derek might have a forum post about this. If not, he's got a great tutorial on using Handbrake there, which is fairly recent.

Edit: Downloaded your sample file. Did as I said above about just dropping on to the timeline, then went to "Render As". Rendered one using the Magix Intermediate HQ 422 3840x2160 (default settings), and one with a QuickTime DNxHR HQ default settings, and both worked when brought back onto the timeline. Sound in both Transcoded files were same as original. The Magix Intermediate file was roughly 3.5 GB, where as the DNxHR was just shy of "Twice" the file size at around 6.84 GB. Playing either on the timeline was smooth enough, though in Preview at Best/Full, showed as only playing between 19-25 fps. But, scrubbing the timeline was "SMOOTH", especially compared to the original file.

All my specs in signature.

Just for your information, a lot of people have had issues in most all of the NLE's with the HEVC codec that GoPro used. Not only what you have with the Hero 7, but also those of us that have the Hero 6 Black and do the 4K60, as it is in HEVC as well. The only thing from GoPro's Support site that I have been able to find concerning this, is actually "re-wrapping" the footage into an .mp4 container using HandBrake. Though, others here would advise against that since you are doing another "compression" of the footage.

I tried taking a sample from my Hero 6 Black at 4K60, bring it into Sony Catalyst Browse (at least it's free), and Transcoding into XAVC-I, which would it in an .MXF wrapper. Didn't work a few months back for me though in Vegas Pro 15 or Movie Studio Platinum 15, though I know there has been some updates to Catalyst since. With only having Davinci Resolve 15 Basic (the free version), since it was 4K60 it would not read it at the time correctly either to Transcode to DNxHR file, again prior to the current 15.2.2 build (I was using an at the time earlier 15.1 something build), so again posssibility.

If you can at least put one clip on the timeline, and do nothing else to the file - no fx, color grade/correction, titles, anything, you might be able to just open up the "Render As", and try either the Magix Intermediate, or what I prefer is the QuickTime 7 DNxHR.

I believe if you go to the Movie Studio Zen website (MovieStudioZen.com), Derek might have a forum post about this. If not, he's got a great tutorial on using Handbrake there, which is fairly recent.

Thank you for the input. It seems to work with proxy files as suggested above. It might be a solution AT LEAST for now..
On the other hand... god damn if Hero 7 would not have great features I would sell it right away and never look back. These issues would not be worth having it.

"It seems to work with proxy files as suggested above. It might be a solution AT LEAST for now.."

I'd submit that your life would be a lot better if you would relieve yourself of the expectation that Vegas or any other NLE will always perform perfectly no matter what herky-jerky machinations camera manufacturers (or screen capture programs or smartphone manufacturers) do to deal with their real or perceived constraints. Magix provided proxies as a way to deal with such issues. Rendering to lossless, more edit-friendly video formats also allows you to complete your task. Here are my results.

GoPro Hero

Vegas Proxies

Magic YUV RGB from SSD

Magic YUV RGB from NVMe disc