W3C home > Mailing lists > Public > public-html-a11y@w3.org > February 2010

Re: timing model of the media resource in HTML5

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Wed, 3 Feb 2010 00:03:45 +1100
Message-ID: <2c0e02831002020503r31fcac6aq66160f5d632f98d6@mail.gmail.com>
To: Philip Jägenstedt <philipj@opera.com>
Cc: Eric Carlson <eric.carlson@apple.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>, Ken Harrenstien <klh@google.com>
On Tue, Feb 2, 2010 at 7:19 PM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Mon, 01 Feb 2010 23:30:19 +0100, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
>> On Tue, Feb 2, 2010 at 3:59 AM, Eric Carlson <eric.carlson@apple.com>
>> wrote:
>>> On Feb 1, 2010, at 4:19 AM, Silvia Pfeiffer wrote:
>>> On Fri, Jan 29, 2010 at 12:39 AM, Philip Jägenstedt <philipj@opera.com>
>>> wrote:
>>> On Wed, 27 Jan 2010 12:57:51 +0100, Silvia Pfeiffer
>>> If we buried the track information in a javascript API, we would
>>> introduce an additional dependency and we would remove the ability to
>>> simply parse the Web page to get at such information. For example, a
>>> crawler would not be able to find out that there is a resource with
>>> captions and would probably not bother requesting the resource for its
>>> captions (or other text tracks).
>>> Surely, robots would just index the resources themselves?
>>> Why download binary data of indeterminate length when you can already
>>> get it out of the text of the Web page? Surely, robots would prefer to
>>> get that information directly out of the Webpage and not have to go
>>> and download gazillions of binary media files that they have to decode
>>> to get information about them.
>>> Right now, everybody who sees a video element in a HTML5 page simply
>>> assumes that it consists of a video and a audio track and has no other
>>> information in it. This is fine in the default case and in the default
>>> case no extra resource description is probably necessary. But when we
>>> actually do have a richer source, we need to expose that.
>>>  This argument leads down a very slippery slope. If it is crucial to
>>> include caption information in markup for spiders, what about other media
>>> file metadata that a crawler might want to read - intrinsic width and
>>> height, duration, encoding format, file size, bit rate, frame rate, etc,
>>> etc, etc? Robots may prefer to have all of this in the page do they don't
>>> have to load and parse the file, but I don't think it is necessary or
>>> appropriate.
>> Not quite.
>> It is a difference if you are a web crawler that wants to collect
>> captions or one that wants to collect such file metadata. For file
>> metadata, you are bound to always be successful when parsing the
>> header of a binary file. So, I agree there with you.
>> But if you are only keen on captions, you are bound to often parse
>> useless information if you have to download the media file header. A
>> hint inside the markup that there are captions/subtitles there and
>> that it is useful to parse the file - and then parse it fully - is
>> very relevant.
> Even if all browser vendors should agree that this is useful and implemented
> the suggested track markup, it will only be used by authors in very rare
> situations -- when they want to populate the browser's context menu before
> HAVE_METADATA. As most videos that have multiple audio/video/text tracks
> won't be marked up as such in HTML, robots will still have to download the
> headers of all videos to see if they have captions. If they want to index
> the captions (not just the fact that they exist), they'll also have to
> download the whole file.

I still believe it's useful to expose the tracks in a media file to
the browser and to automated tools without having to use javascript to
get to them or having to download the media data and decode the

But I don't think any browser vendors will want to implement it at
this stage, so I concede.

Let's instead focus on getting the JavaScript API right and get to a
state where we can at least make use of such multitrack media files.

I have put Eric's proposal with some slight changes (replace "type"
with "role" in the examples, added a "role" attribute, added a "name"
attribute, added a namedItem accessor:

I'd say everyone should free to edit that page as they see fit, but
leave a comment on the mailing list as to why the changes were

Received on Tuesday, 2 February 2010 13:04:38 UTC

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