On Tue, 22 Jan 2002, Billy Biggs wrote: Hello all, Ive been lurking on the mailing list archive for a while (hoping to find some hints about getting a bt848 card to give a colour picture from a pal tuner source), but I have had some experience with the problems mentioned in this thread so here goes.. >> Note that MPEG1 doesn't have an interlaced mode, so if you record a >> 640x480 stream from TV input, you'll see artifacts which bleed between >> the fields. Make sure you're using an encoder which can encode in an >> interlaced mode (like MPEG2) if you want to capture both fields in a >> frame. To avoid those atrifacts, why not seperate the frame into two fields to give twice the fps and then compress that video stream, eg pal 720x576x25fps > 720x288x50fps. On playback every two frames can be re- interlaced to get the original res/fps. >To my mind this doesn't matter if your output display is interlaced >itself. During capture the two fields get assembled into one frame. On >playback the two fields will be reconstructed in their correct time >relationship provided that you blit the frame to the display just at the >start of the first field of a frame time. There can still be problems with this though. A lot of cards have some sort of flicker filter on their tv-outs which averages out 3 or so video memory scanlines to the display. If you want to get output really close to the input, then you need to turn the filter off and make sure, as Steve says, that everything is timed correctly. I am involved a project at the moment which has similar requirements and problems - i need to get dvd quality tv output and the system wasnt able to report which field it was displaying when i started coding. I have found that I can get pretty close (although the interlacing isnt perfect) by using video compressed as described above, leaving the flicker filter on, and blit-stretching each video frame to the full display buffer. It looks pretty close although on some sources the interlacing can look a little stronger than it should. David Pratt
