Hi, my question is relevant to both 525/59.94 and 625/50 but I'll use 525 notation below. The bttv chip writes to memory fields at 59.94hz afaict, however xawtv cannot be convinced to display at this rate. Using XVideo to control the overlay window, all I see is one of the fields. This seems confirmed in the code: height = pPPriv->enc[pPPriv->cenc].height/2; /* no interlace */ And nowhere is there any logic to switch field parity. I'm still trying to figure out how this XVideo driver works and what its purpose is. My assumption right now (please correct me!) is that you're instructing the bttv driver to write frames into video memory, and having the video card use its own overlay code to display it, without any intervention from X or other userspace app. I'm also assuming you're single buffered and never flip. If this is correct, then I guess that's why we only get our half framerate: you have no easy interrupt (or don't use one) to tell the video card to switch its source pointer, and you don't overwrite the top field directly with the second one. I don't understand how you avoid sheering (I guess you don't?). And I don't think the fix is obvious either. If we say screw sheering (or if there's some other reason why that is not an issue), you'd still need some interrupt from the video card to handle the field parity correctly, since you need to start the bottom field a scanline below where you start the top one. If I'm not using XVideo for scaling, just xawtv accessing video4linux directly, then I still don't get true 59.94hz: instead I see interlaced frames! This perplexes me, as I was almost certain that when I bought the card, using xawtv showed me the full framerate video stretching each field independently. Has the xawtv code for this changed at all? I appreciate your thoughts and comments. This issue (why does xawtv look interlaced if not using XVideo, and have poor quality if using XVideo) has come up a few times on #livid. Oh, and one last query, in the v4l XVideo driver source, you use NTSC as '640x480' sampling instead of the traditional '720x480' or the extreme generosity of '768x480' given to PAL (although where those extra samples come from is beyond me). What's up? Thanks, -- Billy Biggs vektor@xxxxxxxxxxxx
