On Sun, 2002-03-10 at 02:30, tony Tong wrote: > what is overlay ? Is it a function of graphic card or > a function of video capture card or both? > Someone told me : > overlay means transfering video from capture card > directly to video memory without cpu's involvement. > Then according to this explaintion ,it should be the > function of both. > But from doc for SDL, I can also see yuvoverlay api. > Does it mean without capture card ,SDL still can > provide the overlay function. > >From this point, overlay should be the function of > video card . It's a function of the videocard. The TV-/capture-card uses this feature to provide a TV-image (the TV-overlay) on the monitor, but it's essentially a feature of the video card. There's more ways that TV-viewing to use overlay, such as video playback (that's wat Xine does, for example) etc. Most of this happens through the X-server's Xv protocol (Xv is the X protocol for handling overlay). > Does overlay means DMA between capture card and video > card or some color space conversion by video card ? > who can give me a answer ? > Any help will be nice ,thanks in advance! TV-card overlay means simply to 'capture' video (overlay is essentially the same as capturing), but instead of capturing video to the mmap()'ed capture memory, you capture straight to the videocard's frame buffer. The action is essentially the same on the capture-/TV-card's side, the result is different though, you don't get 'captured frames' in your mmap()'ed memory but you get the TV-picture on your monitor :-). Ronald -- - .-. - /V\ | Ronald Bultje <rbultje@xxxxxxxxxxxxxxxxxxx> - // \\ | Running: Linux 2.2.19 and OpenBSD 3.0 - /( )\ | http://ronald.bitfreak.net/ - ^^-^^
