On Tue, 24 Aug 2004, Selva Nair wrote:
> I know, but I avoid capture cards that generate "square pixels" from
> non-square pixel sources. As you know PAL or for that matter NTSC frames
It's not generating square from non-square. It's sampling the
analog waveform at a frequency which gives 768 square pixels per line.
A card is free to sample the analog at any frequency it wants. The
DC10+ just happens to be sampling at the rate which gives 768 active
samples per line.
> are not exactly 4:3. I hope the card is padding the frame correctly before
> scaling.
If it's sampling at 14.75MHz then no padding is required - the card
is delivering a 4/3 aspect picture at 768 pixels per line.
> Funny that it cant be convinced to deliver 704x576 or padded 720x576
> frames.
Ah, but 704x576 and 720 are 59:54 pixels, not 1:1. If the card were
sampling at 13.5MHz and generating 704 or 720x576 frames then we
wouldn't be having this discussion :-)
See:
http://www.uwasa.fi/~f76998/video/conversion/
Chapter 3 has a nice table with a lot of useful information. You can
see that 768x576 1:1 size uses a ~14.75MHz sampling rate while the
720x576 and 704x576 59:54 (well, he uses 128/117 but that's close
enough ;)) are using a 13.5MHz sampling rate.
Even though I switched to the DV capture method quite some time ago
I still use y4mscaler a lot when converting HDTV to widescreen DVD
(the scaling's actually more cpu intense than the mpeg2 encoding as
it turns out) and thus need to convert from square pixels to 40:33
for 16/9 DVD.
Steven Schultz
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