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RE: TTML and aspect ratio

From: Michael Dolan <mdolan@newtbt.com>
Date: Wed, 30 Jan 2013 09:52:36 -0800
To: <public-tt@w3.org>
Message-ID: <017801cdff12$981ffda0$c85ff8e0$@newtbt.com>
px really cannot be used for a coded video independence (and it's not
"display", which is entirely unknown to the author).  % is really needed, I
think. 

-----Original Message-----
From: David Ronca [mailto:dronca@netflix.com] 
Sent: Wednesday, January 30, 2013 9:32 AM
To: public-tt@w3.org
Subject: Re: TTML and aspect ratio

> That's not at all obvious to me. Firstly, why would this be different that
<tt tts:extent>? 

<tt tts:extent> specifies the display area.  A client may ignore the pixel
address and only use the computed DAR, but that would be a client-specific
behavior that is undefined in the spec.

> You say you contract out captioning and receive back TTML that contain 
><tt tts:extent='320px 240px'>, is that correct?
Yes, this would be typical.

> So this is 4:3, yes? 

It also means that the dimensions of the root container are 320x240 window,
does it not?

> What would it mean if you had <tt tts:extent='320px 240px' 
> and ttp:displayAspectRatio='16 9'>?

Would not happen.  Also, we would strip out the <tt tts:extent='320px 240px'
> before we deploy the CDN, because our display size varies by stream.

> If you are dynamically generating different media streams to satisfy 
> different clients, why don't you dynamically transform a master TTML 
> document into a display specific document that is targeted to work 
> with the media stream format?

We do not dynamically generate streams.  We generate a set of streams and
various clients will pull streams based on their dynamic bandwidth profile,
which changes frequently.  We would like to generate one caption asset that
can be presented correctly on any device from mobile to a 4K TV.
Received on Wednesday, 30 January 2013 17:53:07 GMT

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