[whatwg] Google Feedback on the HTML5 media a11y specifications

Glenn Maynard glenn at zewt.org
Mon Jan 24 15:45:55 PST 2011

On Mon, Jan 24, 2011 at 4:17 PM, Philip Jägenstedt <philipj at opera.com>wrote:

>  Maybe you could enable them all by default and let users disable the ones
> they don't like?

Few people would use it if the unwanted tracks had to be manually turned off
every time, though.  I know I wouldn't bother.

As far as I'm aware no one has experimented with the rendering parts of
> WebVTT yet. It's defined in <
> http://www.whatwg.org/specs/web-apps/current-work/multipage/rendering.html#rules-for-updating-the-display-of-webvtt-text-tracks>
> and is a little layout engine that tries to avoid overlapping. Implementing
> that and seeing what happens is the best way to find out if it's sane or
> not.
> Do you have a working example of such a multi-conversation scene and how it
> should be rendered? That would be quite interesting to have a look at.

Here's one that I think was done very well, rendered statically to make sure
we're all seeing the same thing:


The results are pretty straightforward.  One always stays on top, one always
stays on the bottom, and most of the time the spacing between the two is
correct--the normal distance the UA uses between two vertical captions
(which would be lost by specifying the line height explicitly).  Combined
with the separate coloring (which is already possible, of course), it's
possible to read both conversations and intuitively track which is which,
and it's also very easy to just pick one or the other to read.

One example of how this can be tricky: at 0:17, a caption on the bottom
wraps and takes two lines, which then pushes the line at 0:19 upward (that
part's simple enough).  If instead the top part had appeared first, the
renderer would need to figure out in advance to push it upwards, to make
space for the two-line caption underneith it.  Otherwise, the captions would
be forced to switch places.

(I don't know how to do this in general while maintaining the goal of
semantic markup over presentation markup, but I think it's worth thinking
about carefully.)

As an aside: the font stroke (the outline around each letter) in the above
clip helps readability substantially.  A solid font color always tends to
blend into the background in places, where a two-color stroked font provides
its own contrast.  I've used the same thing in game UIs rendered on top of a
moving background.  Tangental, but I figured I'd point it out.

Glenn Maynard

More information about the whatwg mailing list