You can create a custom container and publish it, then use that for a “Custom App”. I am not aware whether single nv card would suffice though, since I don’t know whether passing with nvidia container toolkit (to use a card for system resources still) is supported on truenas.
With Intel’s splitting iGPUs it’s very simple, you passthrough a card to container, but system can still use the rest. Though that might not perform adequate for the filters you mention.
With your use-case being the “home theater”, other, more involved solutions may indeed be a better choice.