What is Overlay and why is it fast?
Overlay is the hardware ability of the video card. Usually video image is a bit matrix in the video memory. Each pixel is defined by few bytes in the memory. Overlays allow to show few memory matrixes at the same moment. Processor gives instructions to video card where on the screen the overlay matrix should be placed. And if the pixel has a key color in the screen matrix, video card shows the pixel from the other memory matrix – from overlay matrix. Why are overlays so rapid? Overlays allow to show 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 hardw
