What is overlay?

[trinidav]

What is overlay, and is there a quality difference if it is used?

In MPC, does one mode offer better quality over the next, assuming that a system has the capability to run any of the modes?

[Awatef]

Ok, I'll try to give you a small idea, based on my experience with ZoomPlayer.
For example, the "Overlay Mixer" is fast, but is not suited for downscaling, like watching HD content on lower resolutions like 1024x768.
On the hand, the "Windows Media Renderer", derived in WMR7 and WMR9, offers better quality scaling but is slow.