Re: TTML2 horizontal review with CSS

Hi,

Thanks, David, for the useful analysis of TTML2 and CSS. I was not aware 
of this.

Divergence from CSS should be minimized as we work on a new version of 
TTML. In particular, ease of rendering TTML2 in the web platform by 
converting it in JS to CSS styled HTML should be a key requirement. 
TTML2 needs to be easily implementable in both web and native applications.

Pierre should be able to provide insights into any challenges on 
implementing TTML in HTML/JS, since he's done it for IMSC1.

Best,

-Jim

*Jim Helman * | MovieLabs | o: +1.650.646.2277 m: +1.650.576.1755 | 
*jhelman@movielabs.com * | 475 Sansome St., Suite 740, San Francisco, CA 
94111

On 23/11/2016, 23:33, "L. David Baron" <dbaron@dbaron.org 
<mailto:dbaron@dbaron.org?Subject=Re%3A%20TTML2%20horizontal%20review%20with%20CSS&In-Reply-To=%3CD45C697B.30D6A%25nigel.megitt%40bbc.co.uk%3E&References=%3CD45C697B.30D6A%25nigel.megitt%40bbc.co.uk%3E>> wrote:

>On Friday 2016-11-18 17:48 +0100, Thierry MICHEL wrote:
>> CSS colleagues,
>>
>> The Timed Text Working Group (TTWG) published yesterday an ordinary
>>Working
>> Draft of Timed Text Markup Language 2 (TTML2)
>> W3C Working Draft 17 November 2016
>>https://www.w3.org/TR/2016/WD-ttml2-20161117/
>>
>> FYI, this publication is not the last publication before requesting
>> transition to Candidate Recommendation. The TTWG plans to publish a
>>final WD
>> soon. We will let you know.
>>
>> Meanwhile, the TTWG invites you to review this TTML2 WD.
>>
>> The horizontal review should focus only on the new features
>> introduced in TTML2.
>> Please refer to the section for changes between Timed Text Markup
>>Language
>> (TTML) Version 1 (TTML1) and Version 2 (TTML2).
>>
>>https://www.w3.org/TR/2016/WD-ttml2-20161117/#changes-from-ttml1-vocabula
>>ry
>>
>> Please send your comments to  TTWG Public mailing list
>><public-tt@w3.org 
<mailto:public-tt@w3.org?Subject=Re%3A%20TTML2%20horizontal%20review%20with%20CSS&In-Reply-To=%3CD45C697B.30D6A%25nigel.megitt%40bbc.co.uk%3E&References=%3CD45C697B.30D6A%25nigel.megitt%40bbc.co.uk%3E>>.
>
>So it's worth noting that the styling section of the draft:
>https://w3c.github.io/ttml2/spec/ttml2.html#styling
>has considerable new additions relative to TTML1.  This section
>contains a vocabulary that is rather similar to many CSS properties,
>but also contains significant divergence.
>
>In particular, TTML1 had in
>https://www.w3.org/TR/ttaf1-dfxp/#styling-attribute-vocabulary
>the following styling attributes that appear to match CSS at first
>glance, at least in semantics:
>  backgroundColor
>  color
>  direction
>  display (only auto vs. none)
>  extent (a shorthand for width and height)
>  fontFamily
>  fontSize
>  fontStyle
>  fontWeight
>  lineHeight
>  opacity
>  overflow
>  padding
>  textAlign
>  textDecoration (but with extra values)
>  unicodeBidi
>  visibility
>  wrapOption (like text-wrap in css-text-4)
>  writingMode (but using old values)
>  zIndex
>and the following styling attributes that do not match CSS:
>  displayAlign
>  origin (a bit like x and y in SVG)
>  showBackground
>  textOutline
>
>TTML2 introduces the following new properties that appear to have
>similar CSS properties at first glance:
>  backgroundClip (with different names for the values)
>  backgroundExtent (equivalent to background-size)
>  backgroundImage
>  backgroundOrigin (with different names for the values)
>  backgroundPosition
>  backgroundRepeat
>  border (with border-radius included in the property)
>  bpd (equivalent to block-size in css-logical-properties)
>  fontKerning (though without CSS's initial value, which is auto!)
>  ipd (equivalent to inline-size in css-logical-properties)
>  letterSpacing
>  ruby (this is done using the display property in CSS)
>  rubyAlign (with additional auto, end, and withBase values)
>  rubyPosition (with before/after names instead of over/under)
>  textCombine (equivalent to CSS text-combine-horizontal)
>  textEmphasis
>  textOrientation (but retaining the sidewaysLeft and sidewaysRight
>    values that CSS removed)
>  textShadow
>and the following that appear not to have corresponding CSS properties:
>  disparity
>  fontSelectionStrategy
>  fontShear
>  fontVariant (this is a property name used in CSS, but with a
>    different meaning!)
>  position (this is a property name used in CSS, but with a
>    different value, "center", although one that has been proposed
>    to be added to the CSS property)
>  rubyOffset
>  rubyOverflow
>  rubyOverhang
>  rubyOverhangClass
>  rubyReserve
>
>
>My opinion on this is that this seems like a lot of divergence from
>CSS.  It's divergence in naming (using different names for the same
>thing and the same names for different things), divergence in value
>spaces, and given that everything is redefined in the TTML spec
>(although often non-normatively "based on" CSS specs), almost
>certainly massive divergence in semantics.
>
>I think TTML and CSS have largely been implemented in separate
>implementations (which means that TTML has largely not been
>implemented in browsers), and I don't think TTML1 was designed in a
>way that would fit well in browser implementations.  That's why
>browsers implemented WebVTT instead.  I think continuing to diverge
>from CSS to this degree simply makes TTML implementation in browsers
>even less likely than it already was (which was already unlikely).
>
>On the flip side, I don't think fixing that divergence is
>particularly valuable (at least to browsers) since the communities
>are already separate, and I think the chance of getting substantial
>TTML implementation in browsers is low even without additional
>divergence.
>
>-David
>
>--
>𝄞   L. David Baronhttp://dbaron.org/    𝄂
>𝄢   Mozillahttps://www.mozilla.org/    𝄂
>             Before I built a wall I'd ask to know
>             What I was walling in or walling out,
>             And to whom I was like to give offense.
>               - Robert Frost, Mending Wall (1914)



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*Jim Helman * | MovieLabs | o: +1.650.646.2277 m: +1.650.576.1755 | 
*jhelman@movielabs.com * | 475 Sansome St., Suite 740, San Francisco, CA 
94111