On Thu, 30 Dec 2004, Trent Piepho wrote:
> Yep, and if you divided 640 pixels by 12 3/11 MHz you get 52.15 microseconds,
> the same things you get if you divide 704 pixels by 13.5 MHz.
We could play Oujia board games with the numbers all day long but at
the end of that day the fact remains that square pixel sampling rate
is 12.27...MHz (for 525line systems) and the rectangular is 13.5MHz.
> > TV stations when they are broadcasting a digital stream use 704x480.
> > That's also what they use internally (well, they use 486 lines
>
> Are you sure about that? D1 video is 720 pixels at 13.5 MHz, as specified in
Yes. D1 is 720x486. Fire up the pro tools that can deal with D1
and you'll see the cropping lines - default is to crop 2 pixels at
the top and 4 at the bottom - need to crop the extra 6 lines before
encoding/exporting to DVD, transmission, etc.
D1 is a bit of a misused term though - at one time it really referred
to a digital tape recorder but has since come to refer to the
framesize, etc.
> the ITU-R.601 standard. I know that if you check most (all?) DVDs, you will
> find that they do in fact have 720 pixels (@ 13.5MHz) of information. The 8
Not the ones I make from TV broadcasts (which are 704x480). Why
denoise and encode the extra 2% (especially since they won't be
seen due to TV overscan)?
> pixel border on each side is not just black.
And also not seen on anything except a computer monitor or a monitor
with 'underscan' capability. And when you do see the extra pixels
from material that has been digitized (from old tapes or TV broadcasts)
you'll see that they're junk - they are black or noise in the ones
I've looked at. Coming from film might be different but if it was
from broadcast/tape you'll get the same 704 (more or less) centered
inside a 720 frame.
> There are reasons to get 720 samples when you only care about the inner 704,
Thus 'y4mshift' and other programs to center and border/black and/or
crop. It's better, I've found, to do that then spend the bits
encoding the headswitching and other noise in the area outside the
meaningful 704 pixels. I've seen A LOT of DVDs that are clearly and
plainly transferred from tape that are 704x480 inside a DVD 720x480
frame and there is _junk_ outside the 704.
> But do you know what sample rate your canopus is using? It's supposed to use
> 13.5 since it's DV, but does it? Without datasheets and a driver to dig
Sure - what would you accept as proof? Interoperability with equipment
and software that deals with everything from D1 on up thru DVDPRO-HD?
> through, how can you know?
FUD? Tsk tsk. Try one, measure it - I think you'll find it's closer
to specs than a WinTV card <grin>
I have a lot more confidence that DV gear is doing the right thing
because it is being used in situations where interoperability is
important. You don't see WinTV cards in studios (well, except "Joe's
Garage and Conversion Studio" :)) but you do see Canopus gear.
Folks can sample/capture however they like. For myself there's no
going back - I have seen the difference in quality. Interestingly
I haven't heard of anyone else switching back either - the hard part
is convincing folks to move up in the first place ;)
Cheers,
Steven Schultz
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