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RE: RE: Re: Re: TTML and aspect ratio

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Fri, 1 Feb 2013 16:22:34 +0000
To: John Birch <John.Birch@screensystems.tv>, David Ronca <dronca@netflix.com>, "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <E9A92BD0A4FC934EB7935470A46D15241F55E7B8@DB3EX14MBXC323.europe.corp.microsoft.com>
Well since one doesn't draw actually anything into the root container, except in very simple TTML; what is interesting to me is properly aligning the text content with the underlying video display. 
Now in so much as the root container defines the coordinate system, then I believe the most general system is one that aligns top left 0,0 with 0,0 of the underlying media, and X,Y with the bottom right of the media. Since X and Y can be any real value, it doesn't really matter what value we use so 100%,100% seems adequate. If we then allow negative values and values beyond 100, we can address any relative position.

In such a coordinate system if I want centred left aligned text to appear just below the bottom of the frame; I create a region with alignment centre/bottom, and place it at 50% 90%; if I give it a width of N characters (or better yet define shrink fit regions - a topic for another day); then it works in any aspect ratio.
I can also see utility in being able to have conditional styles, as I may for example want longer text lines in a wide screen presentation (also a topic for another day).

I don't really see is the benefit of changing the 0,0 point, since any transformation I can do to the global coordinates, I can also do by a transform to the region coordinates, but perhaps I am missing something; perhaps you can explain the advantage of moving the root container.

-----Original Message-----
From: John Birch [mailto:John.Birch@screensystems.tv] 
Sent: 01 February 2013 02:07
To: David Ronca; public-tt@w3.org
Subject: RE: RE: Re: Re: TTML and aspect ratio

RE Davids point below and Sean's comment:

"I believe that this scenario does add weight to the case for having tools to position drawing regions where the registration point is other than the top left; and this is open issue 21 http://www.w3.org/AudioVideo/TT/tracker/issues/21."

I disagree with the above... (unless by regions you mean the root container!).

I believe this adds weight to a case for having a mechanism to define the registration point of the root container with respect to any assumed underlying presentation. I.e. a means to specify where the root container origin is located.
Also desirable may be a mechanism to describe how co-ordinates within the root container are scaled against the external context. (e.g. 1:1, scaled to maintain AR, scaled to fit [current behaviour])

Regards,
John

John Birch | Screen | Strategic Partnerships Manager Main Line : +44 1473 831700 | Ext : 270 | Direct Dial : +44 1473 834532 Mobile : +44 7919 558380 | Fax : +44 1473 830078 John.Birch@screensystems.tv | www.screensystems.tv | https://twitter.com/screensystems

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P Before printing, think about the environment-----Original Message-----
From: David Ronca [mailto:dronca@netflix.com]
Sent: 01 February 2013 01:56
To: public-tt@w3.org
Subject: RE: Re: Re: TTML and aspect ratio

Sean Hayes wrote: > What we do stipulate is that whatever mechanism is used, the caption root container should be 100% aligned to the presented video.

This still presents a difficulty.  We have received many 608 captions for content that is 16:9.  In this use case, the root container needs to be a 4:3 area that is the full height of the video window and width is 4/3 height, horizontally centered.



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Received on Friday, 1 February 2013 16:31:52 UTC

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