Vegas doesn't generally support open source codecs. FFV1 is an ffmpeg /libav library.
However, FFV1 is available in a VFW package, which Vegas supports. Find a third party download you trust, install it, and "see if" it shows up as a Video for Windows option in Vegas. I haven't tried to install it personally, since there are other lossless intermediates I use regularly in Vegas.
Note: Voukoder for Vegas has the FFV1 encoder, but that doesn't help you with opening the files in Vegas. Please don't install a codec "pack."
Fwiw, when I ran ffmpeg quality analysis on Zraw transcodes to both lossless hevc and ffv1, they came up with 100% matching across the board with every metric. I've never been able to get Vegas to read ffv1, but it loads lossless hevc just fine.
Thanks Howard and Mark. To date I've not been able to load an FFV1 file. And I do have Voukoder, but as stated it is only encoder of FFV1. I did install the K-lite pack (against recommendations)....and still can not get the FFV1 decoded/loaded. Right now I can only use OpenShot to edit FFV1 files....but I sure like to use the more powerful Vegas Pro. I'm hoping some day Vegas Pro will open these files.
@john-romein I need to refine my statement a bit. FFV1 VFW decoder should be available in the ffdshow library, which carries quite a bit more confidence with editors than K-Lite (which may replace system codecs that Vegas needs).
That said, I would absolutely start with a fresh backup image or Windows installation to be on the safe side. As far as getting rid of K-Lite, you may need to do that anyway. Good luck.
The official Vegas FAQ on ffdshow and codec packs is here.
Thanks Howard and Mark. To date I've not been able to load an FFV1 file. And I do have Voukoder, but as stated it is only encoder of FFV1. I did install the K-lite pack (against recommendations)....and still can not get the FFV1 decoded/loaded. Right now I can only use OpenShot to edit FFV1 files....but I sure like to use the more powerful Vegas Pro. I'm hoping some day Vegas Pro will open these files.
I know that installing -Lite makes Vegas read FFV1 (just like installing the UT Video codec makes it visible to Vegas). But is there an alternative method? I don't really want to install this pack.