Creating a smooth screencast video on iOS from UIView

Question

I've been trying to get my head around recording a screencast, in app, on iOS7. There are some fantastic apps out there, for example Explain Everything (which I'm not trying to compete with, replace or copy), but I can't see how they manage to get such smooth recording of drawing. It looks like they record to their own proprietary format and then export to a movie when requested by the user.

I've tried some libraries:

• Glimpse . Unfortunately it still uses renderInContext and is really slow
• ScreenCaptureView and (what appears to be a derivative) UIScreenCaptureView . The later uses the new drawHierachy methods, but it pimps the iPad's processor up to 96% and is far too slow to draw smoothly; it feels like you're dragging your finger through treacle.

It seems like recording UIView directly to a movie is just too inefficient to create a smooth, drawing based screencast like you see in apps like ShowMe or Explain Everything.

Is there an approach to recording smooth drawing, or what happens in a given UIView that is smooth and achievable? How do (good) screencast apps already out there manage this?

Answer 1

Seems obvious now, but it wasn't at the beginning. The above libraries all use the main thread so I implemented my own solution and used GCD to record on a background thread> This free'd up the interface and stopped the treacle like effect while recording.

Not 100% if it's thread safe or not ( this post seems to indicate that it's not but this post suggests accessing the graphics stack is safe to access). It seems to work for me though. I used a Zoul's solution and drawViewHierarchyInRect:afterScreenUpdates to render the contents of a view in a background thread. It's surprisingly fast and I haven't had any problems yet.