Re: metadata in the VTT file header, re-starting the conversation

On May 13, 2012, at 9:44 , Glenn Maynard wrote:

> On Wed, May 9, 2012 at 7:27 PM, Silvia Pfeiffer <silviapfeiffer1@gmail.com> wrote:
> >  If the
> > information has to be loaded out of each .VTT file, it could require a lot
> > of seeking around the file to load it; slow on optical media, even if it
> > happens to be stored in the same file.
> 
> We're only talking about header-style metadata. There is no seeking
> around required: it comes straight after the WEBVTT magic string.
> 
> Reading data at the beginning of the file is exactly what requires seeking around.  If you're loading metadata for ten VTT files embedded in a WebM file, you have to seek to the location of each embedded file to read it.  That's why formats like WebM store metadata like that in a single index that can be loaded all at once.

Yes, if you fragment a single stream of text into a file like webm or mp4, I would expect to store the header only once.  The TTML habit of making whole valid TTML files for short intervals is Nasty.

> My prediction is that putting metadata like "kind" and "language" in the VTT file will never be done consistently anyway; most people will put it in the HTML, see that it works in browsers, and not bother to put the data in the VTT file too. 

That's fine. Those files weren't intended for standalone use.

> It's easiest to think of it as a caching mechanism.  The only reason to put the data in both the HTML file *and* the VTT file is because it's faster to read it all at once out of the HTML file; the HTML data effectively becomes a cache of the metadata stored in the VTT files.
> 
> So long as the cache is consistent, everything's fine.  It's just unfortunate when the cache gets out of sync (eg. people update one and not the other).

right, so we need to say that the html takes precedence (but please don't do it)


David Singer
Multimedia and Software Standards, Apple Inc.