Re: TextTrackCue discussions

On Mon, Jul 22, 2013 at 9:16 PM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com>wrote:

> That's a fair observation and right now each file format (in
> particular WebVTT) provides for all the semantics through the same
> internal markup. I suppose we can continue creating more WebVTT cue
> settings and markup for all cue kinds for a while before we create
> something that creates a problem. Also, there is not currently a
> specification of a different cue JS object (such as TTMLCue). So,
> let's cross that bridge when we get to it.
>

We are already at that bridge. There is an early draft specification of a
TTMLCue in [1], with editing actions assigned to begin bringing this into
TTML2 ED. There is also development work underway to implement this
functionality in multiple browsers.

[1] http://www.w3.org/wiki/TTML/changeProposal006

That being said, if we had sufficient time on our hands, we could attempt
to merge the semantics of the two different cue formats such that
specifying a single, general purpose interface would suffice. However, the
existing TextTrackCue/VTTCue interface was proposed and implemented without
taking into account the semantics of a TTML based cue. It may turn out that
there is wide overlap, but there may be non-overlapping semantics as well,
and, absent a thorough comparative analysis, we can't yet derive reliable
conclusions.

Our options seem to be:

(1) proceed with defining separate VTTCue and TTMLCue interfaces, possibly
moving common functionality to a their common TextTrackCue interface over
time (future versions);

(2) create a new common interface design after a thorough comparative
analysis of the semantics of the two format's cue semantics;

I would suggest that the first option is more practical and will yield
better short term results. However, since the draft re-charter for the TTWG
includes language to develop a common basis for semantics, then the second
option may be pursued in that context.

G.