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 00:21:20 +1100
Message-ID: <2c0e02831002020521k15518868k810e02dd1802f832@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 12:17 AM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Tue, 02 Feb 2010 14:08:36 +0100, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
>
>> 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?
>
> I quite like Eric's suggestion of exposing this interface on both on the
> media element and on each track. The interface isn't as good as it could be
> yet (e.g. throwing NoValue isn't going to fly, just return undefined) but I
> do think we can reuse this and implement as much of it as possible.
>
> I've already sent some feedback to the Media Annotations WG, but a lot more
> is needed if we want to use this.

Is there a similar API for images that we could compare it with to evaluate?

S.
Received on Tuesday, 2 February 2010 13:22:13 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Friday, 27 April 2012 04:42:01 GMT