[whatwg] WebVTT feedback (was Re: Video feedback)

[Silvia Pfeiffer]

Hi Marc,

On Wed, Jul 20, 2011 at 10:06 AM, Marc 'Tafouk' <wwg at millie.uk.to> wrote:
>
> Hello folks,
>
> I've been following the latest developments on the WebVTT specification and
> am making an attempt to write an out-of-browser parser, using Anna
> Cavender's proposed patches to WebKit.

Cool! Is this a new video player app or going into, say, VLC or
something similar?


> First, I filed a request on the bugtracker
> <http://www.w3.org/Bugs/Public/show_bug.cgi?id=13292> regarding the "end-
> of-file marker" that's mentioned in the current draft
> <http://www.whatwg.org/specs/web-apps/current-work/#webvtt-cue-text-
> parsing-rules>

I replied. IIUC, it's just the EOF state that is meant, not an actual character.


> I have another question about self-closing tags in cue text. It seems
> they're not supported at all.

None of the tags that we have mean anything if they self-close (and
the <timestamp> is implicitly closing).


> The U+002F SOLIDUS character (/) is only handled in the WebVTT tag state.
>
> Test case 1-a):
>   WEBVTT
>
>   00:00.000 --> 00:02.000
>   Initial <b/> test
>
> U+0062 (b) triggers "WebVTT start tag state"; U+002F is then handled as
> "Anything else" and is appended to result (tagname = "b/").

Yes. The next character is then a ">" and causes in the next loop to
return an end tag. Then, end tags are parsed and it's not in the list
that we expect, so this happens: Otherwise, ignore the token. Thus,
<b/> is ignored.


> Test case 1-b):
>   WEBVTT
>
>   00:00.000 --> 00:02.000
>   Initial <b /> test
>
>
> U+0062 (b) triggers "WebVTT start tag state"; U+0020 (space) triggers
> "WebVTT start tag annotation state"; U+002F is handled as "Anything else"
> and is appended to buffer (annotation = "/").

Once ">" is reached, this leads to a start tag <b> with an annotation
of "/". From how I read it, the annotation string gets ignored.


> I am aware those may be moot atm because there is no void element AFAIK,
> and the current tags make no sense when immediately closed.

They still have to parse correctly. But I think from analysing the
spec they actually do.


> I also found a slight issue when following the parser specs : there is no
> validation of the class attribute.

http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#attach-a-webvtt-internal-node-object
says to attach the list of classes to the element. Right now, all
characters are allowed for class names bar space, tab, "." and ">". It
might indeed be an idea to restrict these character to those allowed
for class names in HTML.


> Test case 2):
>   WEBVTT
>
>   00:00.000 --> 00:02.000
>   Second <c.......... [my annotation]> test
>
> classes is a list of 10 empty strings.

While possibly a bit or unneeded overhead, in
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#webvtt-cue-text-dom-construction-rules
when mapping to HTML happens, they just create an additional space in
the class attribute, so are not harmful.


Cheers,
Silvia.