in the screen matrix, video card shows the pixel from the other memory matrix – from overlay matrix. Why are overlays so rapid?
YUV color format. Codecs usually use YUV formats instead of RGB – for better compression. So overlays don’t require YUV->RGB conversions. Overlays provide hardware resizing with filtering. When you stretch the video frame, processor should generate another video frame with different dimensions but when your computer uses overlays it’s not the problem – processor just gives instructions and video card resizes the frame automatically with every monitor refreshing. Also overlays provides hardware clipping. If video window is half-covered by another window, processor should know about covering window’s form and process clipping. But overlay is visible by key color and it hides automatically.
