A GPU with a dedicated encoder for x264 or preferably x265/AV1. You can do without it, but you'll spend a core or two on software encoding and the overhead will

A GPU with a dedicated encoder for x264 or preferably x265/AV1. You can do without it, but you'll spend a core or two on software encoding and the overhead will add a few tens of ms of lag. With full hardware capture and encode (default on windows, can require tweaking on Linux ) it's virtually free resource-wise.