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Re: TTML and aspect ratio

From: David Ronca <dronca@netflix.com>
Date: Thu, 31 Jan 2013 01:33:09 +0000
To: "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <F7DC5134CE82754A878475EEBA450B3B30EB77@EXMB105.corp.netflix.com>
> ok, but now i'm back to why not just use tts:extent, since the AR of the
> root container is nothing more than extent(width) / extent(height)?

Because tts:extent specifies exact pixel container area that the client must use.  If a video starts at 480p, and the tts:extent="640,480", then when the video adaptive-switches  to 720p, and/or 1080p, the caption area (as a percentage of the video) will be reduced, and move towards the top-left.  

We need a caption presentation model that is completely independent of the video.  All positioning must be relative, and the client must know whether to present the captions in a 4:3 area of the video or a 16:9 area.  

David
Received on Thursday, 31 January 2013 01:33:37 GMT

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