Re: Several considerations on implementing WebVTT for media players

On Aug 6, 2012, at 20:24 , Carlos Solís <csolisr@riseup.net> wrote:

> Hello people. I'm not exactly a programmer or anything, just in touch with
> several subtitle communities. And as a matter of personal investigation, I
> have interest in knowing how to build WebVTT subtitles if/when those
> become a standard. However, I am unsure whether WebVTT can be used
> properly outside of a browser, especially the external CSS theming. The
> particular case of desktop video players comes to my mind: is a full HTML
> parser required to implement WebVTT properly in those? Or is a simplified
> CSS parser enough?

My personal read is that you don't *need* any CSS to render VTT.  Using CSS may give stylistic improvement, but semantically the content is self-describing.

> And what about the CSS itself? Is there a way to
> include the CSS theming and the WebVTT cues in a single file, or must the
> CSS be included elsewhere?

We had a thread a while back on header attributes (lines after the WebVTT line but before the first blank line) that terminated in apparent agreement, but I don't think that the spec. has caught up yet.  

That proposed attribute-value pairs, including provision for multi-line values.  We have not decided on the set of attribute names yet, but they probably include
a) information on what you would write in the HTML <track> attributes were you to link this VTT from HTML and
b) applicable style sheets -- either links to, or online -- for this content.

It is not obvious to me that blindly inheriting all the CSS from the page is right, by the way…

> In the second case, embedding the subtitles for
> offline viewing will become harder, as most (if not all) subtitle formats
> are intended to be single-file.
> 
> In a slightly related cue, I've checked how to display simple karaoke. But
> how to theme it properly to scroll smoothly (instead of displaying the
> syllables by chunks), and preview the syllables that will follow (instead
> of showing nothing until the chunk is displayed)? Are the :past and
> :future cues intended to be used for that matter?


We also have a lively discussion that happened on roll-up; if you look at the group's WIKI you'll find a number of options there for how to express roll-up.  Comments appreciated!

Thanks for the interest!

David Singer
Multimedia and Software Standards, Apple Inc.

Received on Thursday, 9 August 2012 22:58:56 UTC