Ok, complete idiot question but couldn't find any mention in the docs.
Does a monitor in record mode always appear black? Tried setting up another monitor in Watch Only but that also appears black while that stream is recording.
Monitor on dashboard goes black and live view in power viewer also black. Tried different codecs, views ok, records ok, just doesn't live view and record simultaneously. New install of Ubuntu with everything updated to latest version.
If this is intentional it might be worth mentioning it somewhere.
Otherwise, incredible what you've managed with node.js.