Thanks for confirming the name/version as described under Help, About.
As has previously been commented VPX8 does not support HEVC video.
Try converting a video clip to a HEVC 8 bit 4:2:0 using Handbrake - I find the conversion improves the contrast and saturation when applying the Canon C-Log3 (from Canon).
Specs should be in the downloadable pdf manual in the program under help.
As others have stated, this is a very old version of VPX. Be careful if you decide to upgrade to the new version as you may need a whole new computer with much higher specs to run it.
There could be a problem if you have reloaded the software as there was a patch that maybe could have enabled the use of your files but the patch may not be able to be updated to.
Thanks for letting us know that updating to VPX15 has resolved the problem for you.
However, your mention of downloading the latest version raises a question in my mind, sorry. Have you bought the upgrade to VPX15? If not, I suspect you are running the Trial version which is feature- and time-limited when compared with the full, purchased version.
Thanks for the update. I'm glad it is running and working for you. I don't think those codecs were implemented in your last version as they were released the same year I think and it takes time for developers to implement them.
It has been the same with the introduction of AV1.
Generally we tend to just post the programs main title. In this case VPX 15 is your new program. Adding which version (the 21.0.1.198 build bit) is harder for people to track down which main version of the program it was if it was before our time of use, or can't find the relevant information on the net to help track down a given programs capabilities due to those numbers are often not added to the internet search engine's results.
Really older versions don't get the additional patches that were supplied back then if the program was bought before the patch came out. You get the version you bought at the time of purchase which meant if an additional patch or upgrade was included, sometimes to a newer version, you didn't get those again once your one year support ended if for any reason you had to reload the program. That has now changed with later released versions and you get all the patches released within the products lifetime but you never get the new version of the program offered within your contract period. The new program is only ever offered at a reduced upgrade price.