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Re: timing model of the media resource in HTML5

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Wed, 3 Feb 2010 00:08:36 +1100
Message-ID: <2c0e02831002020508l1d0cba4fsb6ce727c40ecfb2@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 Wed, Feb 3, 2010 at 12:03 AM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com> wrote:
> 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
> headers.
> 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:
> http://www.w3.org/WAI/PF/HTML/wiki/Media_MultitrackAPI
> 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
> necessary.

Philip: you mentioned
http://www.w3.org/TR/mediaont-api-1.0/#webidl-for-api . Do you think
the track elements should have some of these characteristics, too, and
expose them?

Received on Tuesday, 2 February 2010 13:09:29 UTC

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