W3C home > Mailing lists > Public > public-tt@w3.org > January 2013

Re: TTML and aspect ratio

From: David Singer <singer@apple.com>
Date: Tue, 29 Jan 2013 09:20:39 +0100
Cc: "public-tt@w3.org" <public-tt@w3.org>
Message-id: <CD57A4AB-2B9B-4438-8E12-98B0793166FC@apple.com>
To: Geoff Freed <geoff_freed@wgbh.org>

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

David Singer
Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 29 January 2013 08:21:12 UTC

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