ISSUE-2324 (captioning): media elements in SVG need ability to associate captions and description [SVG 2.0]

ISSUE-2324 (captioning): media elements in SVG need ability to associate  captions and description [SVG 2.0]

http://www.w3.org/Graphics/SVG/WG/track/issues/2324

Raised by: Chris Lilley
On product: SVG 2.0

>From http://www.w3.org/Bugs/Public/show_bug.cgi?id=9697

The <audio> and <video> elements in SVG need to have a peer element to contain
timed text to support captions, subtitles and the text of descriptions. While
an approximation to captions can be done using <animation>, this is not a good
substitute to using a dedicated timed text format and there are no controls for
the user to find them.

Proposal (1)
Allow <foreignObject> to have the Attributes for runtime synchronization so
that for example an external TTML file may be referenced, or an embedded TTML
resource.

Proposal (2) 
Add an explicit <timedText> element equivalent to <video> to provide such
references.

Proposal (3)
Add system properties for captions, descriptions and subtitles in order to
control the rendering of these formats.