Fixed delay between each action on the screen

[probonopd]

Sometimes I need to think when I do screencasts, and still want the screencast to proceed smoothly. Is there a possibility to record only those frames where there is action in the screen, and each at the same delay from the previous frame in which there was action? This would effectively cut out the "thinking pauses".

[zyrolasting]

@probonopd @chjj Working on this. See #27