W3C home > Mailing lists > Public > whatwg@whatwg.org > November 2008

[whatwg] video tag: pixel aspect ratio

From: Ian Hickson <ian@hixie.ch>
Date: Mon, 17 Nov 2008 02:00:17 +0000 (UTC)
Message-ID: <Pine.LNX.4.62.0811170156000.1237@hixie.dreamhostps.com>
On Thu, 13 Nov 2008, Pierre-Olivier Latour wrote:
> 
> And the suggested "hack" is not even really usable: if you have a video coming
> from a NTSC DV source as 720x480 improperly transcoded to say MP4 720x480
> square pixels, using the theoretical 10:11 pixel aspect ratio will _not_ make
> it look right: it needs to be clipped to 704x480 first.

Are you sure? If you don't clip it, you still get the right shape pixels, 
don't you? You don't get the right final video size, sure, because you 
didn't crop, but so what? We're just trying to do a last-ditch aspect 
ratio fix here, not get perfect video.


> Pixel aspect ratio has a precise meaning in the video world, and using 
> it outside of clean aperture does not make a lot of sense...

As far as I can tell, using it outside clean aperture works fine so long 
as you don't also expect the final output to be the "right" video size.


> At the same time, saying that pixel ratio is intentionally ill-defined 
> because we don't *really* want people to use it is also quite confusing.

Right, that's the idea. :-)


> If we start going in this direction, then <img> should have a "dpi" 
> attribute so you can "hack" around images uploaded at dpi > 72 ;)

We effectively do, it's the "height" (or "width") attribute.


> In any case, if this attribute really needs to be present, we should 
> rename it at the minimum (picking a term from the "professional" video 
> world requires taking the constraints that come with it), maybe 
> "displayRatio" or something?

Maybe horizontalpixelstretchfactor?

Personally I don't really see the problem with "pixelratio".

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Sunday, 16 November 2008 18:00:17 UTC

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