Yeah absolutely, I should have emphasised - so it relies on you transcoding first into prores.Aferburner is even more limted than that: only ProRes codec & somthing not all that common in cameras. A good Nvidia would have nailed it, but oh …. Useless except for a specialised & questionable workflow. Yet another dubious brain fart & misrepresentation from Apple.
They certainly marketed it as a reconfigurable piece of hardware, as if it would be able to be reconfigured in realtime on a task by task basis.