On Wed, 29 Dec 2004, Ray Cole wrote: > > a single frame in probably > 200 hours of recording). I tell it to capture > at 720x480 and I haven't noticed any distortion. Should I really be > capturing at 704x480 instead? I don't do any scaling beyond the capture > phase and it all looks fine to me, so I assume I'm OK, but could give > capturing at 704x480 a shot.
See this, http://www.arachnotron.nl/videocap/site/capture_area2.html In short, if you are converting to DVD, you want to tell your card to capture at 13.5 MHz. This is the rate specified in the standards and the rate the DVD will be played back at. Most capture card drivers have a fixed idea about what length of a line, in microseconds, they should capture. If the driver thinks is should capture a line 53.33 us long, then 720 pixels gives you a sample rate of 13.5 MHz. If the driver thinks a line is 52.15 us long, then you only get 704 samples. Finally, a 52.67 us long line is 711 samples at 13.5 MHz. All of those line length are used by something. 53.33 was specified by CCIR-601 and is used by DVDs, SVCDs, DV, and professional systems. 52.67 is the active length as specified in the NTSC standard, and is also used in the bt848 datasheet. 52.15 is used by VCDs, DVDs in 704x480 mode, and 640x480 square pixel captures. So which does you card use? If you look at that page, they have a DVD or SVCD test track which you can play on a DVD player. Capture it and compare to the original image. By comparing the scale lines, you can tell what you card is doing. Of course, if you have an open source driver, you can just look at the source to see what the driver is using, and change it to the correct value for what you want. ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ Mjpeg-users mailing list Mjpeg-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mjpeg-users
