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[whatwg] video tag: pixel aspect ratio

From: Sander van Zoest <sander@vanzoest.com>
Date: Wed, 15 Oct 2008 08:52:18 -0700
Message-ID: <98c2a8300810150852r44f45987n8a3f7d0303258592@mail.gmail.com>
On Wed, Oct 15, 2008 at 8:14 AM, Anne van Kesteren <annevk at opera.com> wrote:

> On Wed, 15 Oct 2008 17:01:22 +0200, Sander van Zoest <sander at vanzoest.com>
> wrote:
>
>> I hate to say it, but if it was enough, I wouldn't be commenting here. It
>> simply isn't accurate
>> enough to store it as a float.
>>
>
> How is not accurate? In terms of precision it shouldn't really matter...


We are talking video here. Precision is at its core. If you consider the
majority of the broken
video out on the net today a good example of what you want more of then, I
see no reason
to accurately define PAR. I won't get into Frame Rates such as 59.94Hz,
since that is off topic
here, but you can not accurately convert video on the fly if you do not have
the exact ratio. All
this stems from the conversion from analog to digital and in the analog
world we did a lot of funky
tricks to make things work better on hardware of those days, but as our
computers and electronics
in general get faster and faster, putting in inaccuracies can cause for some
seriously ill side effects,
now and especially in the future. Because of the conversion from analog to
digital there are a lot of funky areas where you end up with a PAR/SAR that
would be rounded inaccurately if expressed as a float. 2 32-bit
integers is what is used today, with the hope that that will get us into a
fully square pixel world, by the time
the video quality gets good enough where we can no longer express PAR in
32-bit integers.

For some background on this see <
http://lipas.uwasa.fi/~f76998/video/conversion/>. I really do not want to
add to the inaccuracies in the world, especially if we have a chance to do
it right.

There are already many of these types of mistakes in things like Media RSS,
I wouldn't know how to accurately express the frame rate of a 30M clip in
the framerate attribute of the content element. For some of the madness that
we are talking about here, see <
http://groups.google.com/group/sci.engr.advanced-tv/msg/108815e3089c4d53?pli=1>.


I am sort of of the camp, if you are going to even provide pixelratio as an
attribute, then at least do it like every other container format out there,
rather then expressing it a manner that limits its use and forces
inaccuracies caused by rounding and human error (because they do not
understand why you want a 10 digit float).

Take it for what it is worth.

-- Sander
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