Re: TextTrackCue discussions

On Mon, Sep 16, 2013 at 12:36 PM, Jerry Smith (WINDOWS) <> wrote:

>  File based caption scenarios work fine with a format agnostic cue
> object, which suggests your concern about loss of essential semantics
> involves dynamically created cues.

At present, all of the content related attributes/operations on
TextTrackCue/VTTCue are format specific in their semantics and possibly

text - both syntax and semantics differ, given returned text is format

getCueAsHTML() - returned DocumentFragment is expected to have different
structure and use different mapping for different formats; at present, no
constraints are specified on the returned fragment, e.g., whether it is
acceptable for parenting to HTMLDivElement, etc;

immediate style attributes - those that have moved from TextTrackCue to
VTTCue are all WebVTT format specific;

Consequently, I don't see any difference between file based (out-of-band)
and in-band scenarios as far as whether a cue interface is format specific
or not. The old TextTrackCue is format specific (WebVTT), and the new
VTTCue is format specific (WebVTT). However, the new TextTrackCue is format

> A lot could be done for these by supporting formatted XML or some other
> format fragment on the text cue.  This would require format specific
> support in the browsers, like media files do with media elements now.
> That’s true with format specific cues as well, like the proposed VTTCue.
> Do you believe doing this would lose support for essential format specific
> semantics?
I expect that TTMLCue will expose a reference to an XMLDocument
representing the parsed TTML XML DOM. While there are some renderable
formats (e.g., smilText) and metadata formats (e.g., MPEG7) that also use
XML, and that could be exposed in a similar fashion, most
caption/subtitle/metadata formats use either format specific plain text
formats or binary formats.

> ** **
> Jerry****
> ** **
> *From:* Glenn Adams []
> *Sent:* Thursday, September 12, 2013 7:17 PM
> *To:* Jerry Smith (WINDOWS)
> *Cc:* Brendan Long; Silvia Pfeiffer; HTML WG (
> *Subject:* Re: TextTrackCue discussions****
> ** **
> ** **
> On Fri, Sep 13, 2013 at 2:32 AM, Jerry Smith (WINDOWS) <
>> wrote:****
> Is there an assumption that thin or thick TextTrackCues would be for text
> only representations?  The existing cue definition (not the newer drafts)
> can adequately source styled cues and works with getCueAsHTML on separate
> WebVTT or TTML caption files.  For compatibility reasons, these should
> continue to work.
> The use of format specific cue objects like VTTCue may allow tuned
> attributes for a specific format, but they also fragment the programming
> model and make it more difficult for websites to support content with mixed
> caption formats, do they not?
> I have had some side discussions with Silvia and others about the
> overarching goals of this revision.  Some have replied that it is to focus
> format specific syntax and features on objects that clearly have a format
> specific intent.  That would seem predicated on an assumption that a format
> agnostic solution, usually the desired goal for web specifications, is not
> possible.  Do we agree that is the case?****
>  ** **
> IMO, a single format agnostic cue interface is impractical, and, if
> imposed from without, will result in necessary loss of essential format
> specific semantics. However, the TTWG hasn't specifically considered this
> point, so it would be useful to pose the question there to determine if my
> opinion is shared.****
>  ****
> Jerry****
> -----Original Message-----
> From: Brendan Long []
> Sent: Monday, September 9, 2013 9:03 AM
> To: Silvia Pfeiffer
> Cc: HTML WG (
> Subject: Re: TextTrackCue discussions
> On 09/08/2013 06:41 PM, Silvia Pfeiffer wrote:
> > That would require converting DVD raster graphics to an img format
> > that the browser understands. Once a browser implements that, there
> > are likely other attributes that it will implement, so a specific
> > DVDCue interface would be created.
> I agree. My point is that if we create a new DVDCue class, it should be
> required to implement getCueAsHTML().
> > [Constructor(double startTime, double endTime, DOMString text)]
> > interface GenericCue : TextTrackCue {
> >            attribute DOMString text;
> >   DocumentFragment getCueAsHTML();
> > };
> This is basically what I had in mind, although personally I would put
> .text in TextTrackCue, since all cues should have it, whether the browser
> can parse them or not, right?
> > enum AutoKeyword { "auto" };
> > enum DirectionSetting { "" /* horizontal */, "rl", "lr" }; enum
> > AlignSetting { "start", "middle", "end", "left", "right" };
> > [Constructor(double startTime, double endTime, DOMString text)]
> > interface TextCue : TextTrackCue {
> >     attribute DirectionSetting vertical;
> >     attribute boolean snapToLines;
> >     attribute (long or AutoKeyword) line;
> >     attribute long position;
> >     attribute long size;
> >     attribute AlignSetting align;
> >     attribute DOMString text;
> >   DocumentFragment getCueAsHTML();
> > };
> It would be nice if we could assume all cue formats support this
> interface, but from Glenn and Simon's responses, it doesn't sound like
> that's realistic. I think there's nothing wrong in principle with using
> WebVTT's semantics where other format support it though, since consistency
> is extremely useful.
> > I'm now thinking .text could be restricted to just plain text. Thus,
> > I've moved getCueAsHTML() into these interfaces, too, seeing as it
> > could simply return a DocumentFragment with plain text.
> Isn't .text used in unparsed cues though? It seems dangerous to return
> unparsed cue content in getCueAsHTML(), since that would make it easier for
> JS developers to accidentally render unparsed cue content (which would be
> particularly annoying with something like CEA708, where the unparsed
> content is binary, probably base64 encoded in .text).****
>  ** **

Received on Monday, 16 September 2013 19:00:54 UTC