IOSurfaces - Artefacts in video and unable to grab video surfaces

Question

This is a 2-part Question. I have the following code working which grabs the current display surface and creates a video out of the surfaces (everything happens in the backg

Answer 1

I did a bit of experimentation and concluded that the screen surface from which the content is copied is changing even before the transfer of contents is complete (call to IOSurfaceAcceleratorTransferSurface() ). I am using a lock (tried both asynchronous and read-only) but it is being overridden by the iOS. I changed the code between the lock/unlock part to the following minimal:

IOSurfaceLock(screenSurface, kIOSurfaceLockReadOnly, &aseed);
aseed1 = IOSurfaceGetSeed(screenSurface);
IOSurfaceAcceleratorTransferSurface(outAcc, screenSurface, destSurf, dict, NULL);
aseed2 = IOSurfaceGetSeed(screenSurface);
IOSurfaceUnlock(screenSurface, kIOSurfaceLockReadOnly, &aseed);

The GetSeed function tells if the contents of the surface have changed. And, I logged a count indicating the number of frames for which the seed changes. The count was non-zero. So, the following code resolved the problem:

if(aseed1 != aseed2){
//Release the created surface
continue; //Do not use this surface/frame since it has artefacts
}

This however does affect performance since many frames/surfaces are rejected due to artefacts. Any additions/corrections to this will be helpful.