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Re: video size when aspect ratio is not 1

From: Philip Jägenstedt <philipj@opera.com>
Date: Mon, 14 Sep 2009 09:47:37 +0200
To: "Ian Hickson" <ian@hixie.ch>
Cc: "Simon Pieters" <simonp@opera.com>, "public-html@w3.org" <public-html@w3.org>
Message-ID: <op.uz8k9nhtatwj1d@sisko.linkoping.osa>
On Mon, 14 Sep 2009 08:48:59 +0200, Ian Hickson <ian@hixie.ch> wrote:

> On Thu, 3 Sep 2009, Philip Jägenstedt wrote:
>> On Thu, 03 Sep 2009 13:47:41 +0200, Ian Hickson <ian@hixie.ch> wrote:
>> > On Mon, 31 Aug 2009, Simon Pieters wrote:
>> > >
>> > > The following paragraph:
>> > >
>> > > "The intrinsic width and intrinsic height of the media resource are
>> > > the dimensions of the resource in CSS pixels after taking into
>> > > account the resource's dimensions, aspect ratio, clean aperture,
>> > > resolution, and so forth, as defined for the format used by the
>> > > resource."
>> > >
>> > > ...doesn't say whether to scale up or down when taking into account
>> > > aspect ratio.
>> >
>> > Wouldn't that be up to the video format?
>>
>> No, video formats only give the size in pixels and the pixel aspect
>> ratio (or alternatively frame aspect ratio). The only constraint is that
>> the aspect ratio be correct, which forces us to choose how to achieve
>> that. Assuming one dimension remains unchanged:
>>
>> 1. always scale up
>> 2. always scale down
>> 3. always scale x-dimension
>> 4. always scale y-dimension
>>
>> We're suggesting #1. From the rest I've only seen #3 used in actual
>> media players.
>
> Fair enough. I've specced #3 (#3 and #4 are simpler to implement than #1
> or #2, and the extra complexity doesn't seem to gain us much. I've never
> heard of anamorphic video data with a ratio less than 1.0, so assuming my
> experiences are representative, it's the same as #1 in most cases  
> anyway).

Actually, standard 720x480 4:3 NTSC DVD video has an pixel aspect ratio of  
8:9 and there is no shortage of it. While #3 is easier to both spec and  
implement, both we and Mozilla have already independently chosen to  
implement (and write tests for) #1, so I'd much prefer if that were  
specced. Chrome seems to not do anything and I don't know how to produce a  
suitable test file for Safari.

-- 
Philip Jägenstedt
Core Developer
Opera Software
Received on Monday, 14 September 2009 07:48:17 UTC

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