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Re: TTML and aspect ratio

From: Geoff Freed <geoff_freed@wgbh.org>
Date: Tue, 29 Jan 2013 16:11:08 +0000
To: David Singer <singer@apple.com>, "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <A3CD72FE7CF8DE4B953A034D1982200C2FFE0ADE@WSMBX1.wgbh.org>

Hi, Dave (and others who replied separately):

I think what they want to do is faithfully reproduce 608 (4:3) or 708 (16:9) captions that have been converted *to* TTML, and to retain authorial intent so the captions have the same look as originally created.  In other words, they want to declare that the original data came from either a 608 or 708 stream, and then let the UA place the captions in the appropriate safe-title area.  I think the current method provided by TTML isn't constrained enough for what they want to do.  I'll encourage them to send someone to the WG list and join this conversation.

More soon.
Thanks.
Geoff


On Jan 29, 2013, at 3:20 AM, David Singer <singer@apple.com> wrote:

> 
> On Jan 28, 2013, at 23:09 , Geoff Freed <geoff_freed@wgbh.org> wrote:
> 
>> 
>> Hi, everybody:
>> 
>> One of NCAM's partners (Netflix) is looking for a way to specify aspect ratio in a TTML file; however, TTML currently has no way of actually specifying aspect ratio.  
> 
> What aspect ratio do you want?  The picture aspect ratio is specifiable, and a pixel aspect ratio is irrelevant (but nonetheless specifiable in TTML), as the text stream does not (unlike video) consist of pixels.  All we need to know is the measurement on uniformly sampled axes, and if it's displayed on a screen with non-square pixels, the system needs to map the measurements.  All that a pixel aspect ratio does is allow us to measure the width and height on non-uniformly-sampled axes, which is maybe a convenience but can be confusing.
> 
> 
>> I took a look through the WG archives and saw that this topic has been discussed recently (http://lists.w3.org/Archives/Public/public-tt/2012Oct/0061.html) but it doesn't look like there has been any resolution.  Is this feature under consideration?
>> 
>> (Netflix has raised the same issue with WebVTT, and it looks like that spec will be including metadata for specifying aspect ratio:  https://www.w3.org/Bugs/Public/show_bug.cgi?id=20566 .)
>> 
>> Thanks.
>> Geoff Freed
>> NCAM/WGBH
>> 
> 
> David Singer
> Multimedia and Software Standards, Apple Inc.
> 
Received on Tuesday, 29 January 2013 16:11:46 GMT

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