While that might be a workaround, it is not a solution or an explanation for the symptoms, unless this is 'expected' behaviour? Ticket was submitted on the 2nd of June, with no update other than a suggestion to use a media player with an output to a physical HDMI, and loop it back in via HDMI capture, instead of using screen capture. Lots of frame skipping as soon as I start.
This behaviour is seen when I do screen capture from an external display. A recent case number is #00748041- and this affects full screen capture too.