The former would be more elegant but the latter is also fine for my purposes (and probably the more errorproof solution).
I capture 720p50-HDTV losslessly (ULH0/ULH2) and my archive-drive is fast enough but as soon as one additional process starts accessing the drive, I get dropped frames and out-of-sync audio which I really want to avoid.
You can use Process Hacker, it gives you an option to save IO priorities for processes.
If ProcessHacker is running in background, the next time your tool gets started, it changes the IO priority automatically to the stored value.
Normally all processes have
normal IO priority, so set your recording tool to