I just tried to record video in “Offline” mode. I get audio when I select “Built In Mic’ as audio input. The only other option was “Unk Device”, which provided no audio output when selected.
Also selected “Serato Video Post Mix” output
Does anything get printed from Syphon Recorder to the console (in /Applications/Utilities/Console) when you start a recording with the Numark device? That might give me a clue to the problem.
I have recorded quite a few video mixes using syphon recorder and my work around for that is to route my rane/akai mixer outputs into my spare sl3 box and it comes up as an input into syphon recorder. I plug the sl3 in after the rane/akai is already up and running. This has been my work around recording video mixes to capture sound and audio in 1 take. The other work around is to record the mic and you monitor speakers and to press record within serato dj then use an app like Adobe premier to hot swap the aiff file Sdj makes with the crappy mic recording 🙂