On Wed, 29 Dec 2004, Trent Piepho wrote:
> See this, http://www.arachnotron.nl/videocap/site/capture_area2.html
Ah yes - forgot about that, been a while since I visited that site.
> bt848 datasheet. 52.15 is used by VCDs, DVDs in 704x480 mode, and 640x480
> square pixel captures.
Hmmm, for square pixel sampling the frequency is not 13.5MHz - it's
12.2727 (actually 12 + 3/11) MHz.
Page 97 in Charles Poyton's "Digital Video and HDTV" (ISBN
1-55860-792-7) - a bible for anyone interested in the field of digital
video.
That's also where (in case you've wondered about that 10:11 number
that keeps popping upc) 10:11 SAR comes from. It's the ratio of the
square and Rec.601 sampling frequencies, work out (12+3/11) / (13+1/2)
and you'll see a 10/11 pop out at the end of the arithmetic ;)
TV stations when they are broadcasting a digital stream use 704x480.
That's also what they use internally (well, they use 486 lines
internally but the extra lines get removed before transmission) in the
analog processing. It doesn't make sense to get 720 samples where
only 704 were broadcast. Does it?
> 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
It might also be possible to dig around in the bttv-driver.c module
in the kernel and combine that with the Bt8x8 datasheets (which I had
but tossed out some time ago) to figure out what is going on. I
vaguely remember registers in the Bt8x8 that were used to specify
the sample size (square, 10:11, etc) but that was a long time ago.
All in all it's an area I'm glad I moved out of :)
Cheers,
Steven Schultz
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