Noise reduction is a big one. You usually need to interpolate over several frames to do that. Also depending on the bus being used cameras often compress the i

Noise reduction is a big one. You usually need to interpolate over several frames to do that. Also depending on the bus being used cameras often compress the image using JPEG to reduce the bandwith (very common with USB cameras, I doubt that the Mac camera does that). Then on a computer you have the latency of whatever pipeline is being used and how much buffering is involved. For instance since typically the display doesn't run exactly synchronized with the camera you'll have some frames that'll end up "stuck" waiting for the monitor's vsync. If the app then does some internal buffering on top of that you can very easily reach a noticeable amount of latency. In general you can consider than anything above 100ms is easily noticeable and that's only 3 frames at 30fps and 6 at 60, it's really not that much when you consider the complexity of modern video capture pipelines.