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[whatwg] video tag: pixel aspect ratio

From: Sander van Zoest <sander@vanzoest.com>
Date: Wed, 15 Oct 2008 08:01:22 -0700
Message-ID: <98c2a8300810150801y79514cc2p56a431ede6cd562b@mail.gmail.com>
On Wed, Oct 15, 2008 at 2:40 AM, Ian Hickson <ian at hixie.ch> wrote:

> On Tue, 14 Oct 2008, Sander van Zoest wrote:
> >
> > I just recently started looking at HTML5 and noticed the video tag. Neat
> > addition. I also noticed that it as an attribute named 'pixelratio',
> > however, as you know this is never an integer, but rather is the result
> > of a fraction (i.e. ratio). As for proper playback of video frames, it
> > is important to understand exact float and therefore I would suggest
> > either expressing it as a ratio of two 32-bit integers separated by a
> > colon (or slash) or use two different attributes. This avoids
> > unintentional rounding.
> >
> > Something roughly along the lines of:
> >
> > <source pixelratio="10:11"> <!-- 525 composite NTSC -->
> > <source pixelratio="59:54"> <!-- 625 composite PAL -->
> > <source pixelratio="1018:1062"> <!-- 1920x1035 HDTV SMPTE RP 187-1995 -->
>
> Currently pixelratio is a floating point number, as in:
>
>   <source pixelratio="0.909090909"> <!-- 525 composite NTSC -->
>   <source pixelratio="1.09259259"> <!-- 625 composite PAL -->
>   <source pixelratio="0.958568738"> <!-- 1920x1035 HDTV SMPTE RP 187-1995
> -->
>
> Is that not enough?
>
> This isn't expected to be used often. It's really only provided to allow
> for simple override of the actual value in the video file, for when the
> video file is known to be wrong. I am very reluctant to make up a whole
> new microsyntax and corresponding parser algorithm, along with all the
> tests, etc, to handle this one case.


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. Every respected container stores the ratio as
X x Y.
See the PASP atom for example.

-- Sander
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