There are certain updates required for Resolve to work with H264 under Win 7, so I wouldn't be surprised if it needs others to fully work
DVC Built Clevo P775DM3-G Laptop with UHD screen, 7700K CPU@4.9Ghz, Geforce GTX 1060 6GB GPU, G-Sync UHD screen, 500GB M.2 Primary, 1x 480GB SSD, 1x1TB M.2, 1x 2TB Video drives. Building Bespoke Video Editing systems for over 16 years
"Saying it is good, but doing it is better! " Win10-1809 | Resolve Studio V16.1 | Fusion Studio V16.1 | Decklink 4K Extreme 6G | RTX 2080Ti 431.86 NSD driver! |
We know that certain H.264 related files will not work with Resolve 12.5.1 or higher on Win7 without this Windows update being installed: https://support.microsoft.com/en-sg/kb/2670838
If you can't update the PC, you might try Resolve 12.5 and see if that works.