So if you have h264 i have no idea why you have this problem with the permission.
You have 2 options with my tutorial
1:
If you have a NAS you can try to mount media to network share
2:
Go to the host machine and check if there is a permission error, if it is , just do as in tutorial but don’t change fstab, but change the /mnt/data/supervisor/media permission with chmod +x
Tutorial:
https://community.home-assistant.io/t/solved-hassos-mount-nas-network-share/
I’m pretty sure you cant change anything in frigate addon as it recreates it self each time.I spend to much time ti figuring it out.