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Re: Agenda+ review 1st WD of WebVTT

From: Simon Pieters <simonp@opera.com>
Date: Tue, 31 Mar 2015 13:26:56 +0200
To: "David Singer" <singer@apple.com>, "Bert Bos" <bert@w3.org>, "Alan Stearns" <stearns@adobe.com>
Cc: "www-style@w3.org" <www-style@w3.org>
Message-ID: <op.xwc0q6woidj3kv@simons-mbp>
(Again move technical discussion to the public list....)

On Tue, 31 Mar 2015 13:19:30 +0200, Simon Pieters <simonp@opera.com> wrote:

> On Mon, 30 Mar 2015 23:22:58 +0200, Alan Stearns <stearns@adobe.com>  
> wrote:
>
>> On 3/30/15, 1:37 PM, "David Singer" <singer@apple.com> wrote:
>>
>>> It would be nice to get the CSS group’s feedback, or individual  
>>> feedback,
>>> soon.
>>>
>>> We’re working on providing style-sheets in the CSS file (probably the
>>> most-sought ‘missing feature’ from this review).
>>>
>>>
>>>> On Feb 20, 2015, at 5:04 , Bert Bos <bert@w3.org> wrote:
>>>>
>>>> On Thursday 19 February 2015 07:28:01 fantasai wrote:
>>>>> On 02/18/2015 12:36 PM, Tab Atkins Jr. wrote:
>>>>>> On Wed, Feb 18, 2015 at 9:34 AM, Sylvain Galineau
>>>>>> <galineau@adobe.com>
>>>> wrote:
>>>>>>> All this feedback seems technical. Did I miss the reason it’s
>>>>>>> happening on this list?
>>>>>>
>>>>>> We sometimes gather feedback and then send it as a group?  I thought
>>>>>> that's what was happening here.
>>>>>
>>>>> We still gather it on www-style...
>>>>
>>>> The list for discussions of WebVTT is <public-tt@w3.org> and that is
>>>> also
>>>> where the TTWG asks us to send our group's comments. (See the slide
>>>> called
>>>> "Reviews" in https://www.w3.org/2015/Talks/0212-WebVTT/)
>>>>
>>>> Each of us can join that list and send personal comments, too, but the
>>>> TTWG
>>>> asked for our comments as a group and I agree with them it is more
>>>> efficient
>>>> that we discuss first among ourselves and then send them the outcome.
>>>> That's
>>>> why I asked to put it on the agenda.
>>>>
>>>> It doesn't mean we need to have consensus on our comments.
>>>>
>>>>
>>>> I think the comments so far are already very useful. I volunteer to
>>>> draft a
>>>> response to the TTWG, after we discussed them a bit more.
>>
>> My comment for the collection is either on WebVTT or CSS Text level 4.  
>> The
>> definitions for line balancing should be rationalized, and probably a  
>> note
>> should be added to both that the definition may only hold for Latin  
>> text.
>>
>> In WebVTT section 6.1 [1], step 11 of the algorithm for obtaining CSS
>> boxes says:
>>
>> -----
>> any line breaks inserted by the user agent
>> for the purposes of line wrapping must be
>> placed so as to minimize Δ across each run of
>> consecutive lines between preserved newlines
>> in the source. Δ for a set of lines is defined
>> as the sum over each line of the absolute of
>> the difference between the line's length and
>> the mean line length of the set.
>>
>> -----
>>
>> In Text level 4 section 5.1 [2], the definition of text-wrap:balance  
>> says:
>>
>> -----
>>
>> Line boxes are balanced when the standard deviation from
>> the average inline-size consumed is reduced over the block
>>
>> (including lines that end in a forced break).
>>
>> -----
>>
>>
>> I’d be happy to adopt WebVTT’s second sentence if that’s deemed better,
>> but I’m not that happy about the first sentence. If you assume a forced
>> break is always a paragraph boundary, then different line lengths before
>> and after the break are fine. But if you consider a forced break to not
>> break apart the paragraph, then different line lengths before and after
>> the break are bad.
>
> I think it would be good if WebVTT used text-wrap:balance instead of its  
> own prose to handle line balancing, so UAs can have a single  
> implementation for both WebVTT and CSS.
>
> I don't have a strong opinion on what the rule should be, but for CSS it  
> would be good if it allows an implementation to balance many lines of  
> text with acceptable performance (e.g. O(n^2) is not acceptable).
>
> Also see https://www.w3.org/Bugs/Public/show_bug.cgi?id=19458
>
>> Thanks,
>>
>> Alan
>>
>> [1] http://dev.w3.org/html5/webvtt/#processing-model
>> [2] http://dev.w3.org/csswg/css-text-4/#text-wrap
>
>


-- 
Simon Pieters
Opera Software
Received on Tuesday, 31 March 2015 11:27:25 UTC

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