Replied by DoctorZen on topic Which versions of Vegas Movie Studio can edit 4K video?
You can't edit 4k video with version 12.
Yes you will need to upgrade to Vegas Movie Studio Platinum 16.
Version 16 also uses the newer Magix AVC encoder/decoder, which is optimised to work with the latest Nvidia and AMD Radeon graphics cards.
If you don't have a powerful enough CPU and Graphics Card, you will struggle to edit 4k video with Vegas.
I recommend you download the free trial for v16 and test it out before you upgrade.
If you do decide to upgrade, use the Ad link at bottom of this page to get the best discount on Vegas.
Remember to turn everything off at least once a week, including your brain, then sit somewhere quiet and just chill out.
Unplugging is the best way to find solutions to your problems.