[whatwg] metadata attribute for media

[Ralph Giles]

Recently, we've been considering adding a 'tags' or 'metadata' attribute
to HTML media elements in Firefox, to allow webcontent access to
metadata from the playing media resource. In particular we're interested
in tag data like creator, title, date, and so on.

My recollection is that this has been discussed a number of times in the
past, but there was never suffient motivation to support the interface.
Our particular motivation here is webapps that present a media file
library. While it's certainly possible to parse the tag data out
directly with javascript, it's more convenient if the HTML media element
does so, and the underlying platform decoder libraries usually provide
this data already.

As such I wanted to raise the issue here and get design feedback and
levels of interest for other user agents.

Here's a first idea:

partial interface HTMLMediaElement {
  readonly attribute object tags;
};

Accessing media.tags provides an object with a key: value data, for example:

{
  'title': 'My Movie',
  'creator': 'This User',
  'date': '2012-06-18',
  'license': 'http://creativecommons.org/licenses/by-nc-sa/'
}

The keys may need to be filtered, since the files can contain things
like base64-encoded cover art, which makes the object prohibitively
large. The keys may need to be mapped to some standard scheme (i.e.
dublic core) since vocabularies vary from format to format.

This is nice because it's easy to access, can be simply enumerated,
and extensible. Which is helpful when if gets added the <img> for exif data.

 -r