Comment by dnet

Not sure about VLC, but ffmpeg has great support for Blackmagic, you just have to download the Blackmagic SDK, compile ffmpeg with Blackmagic support (and the SDK in path) and then you'll have a separate input/output device available in ffmpeg. The other great thing about this approach is that this way audio also takes a dedicated, integrated path, bypassing OS layers and maintaining sync with much less effort.