W3C home > Mailing lists > Public > public-html-a11y@w3.org > February 2011

Re: [media] Displaying Multitrack Video (issue-152)

From: David Singer <singer@apple.com>
Date: Thu, 24 Feb 2011 15:11:30 -0800
Message-Id: <0206D2CC-48C9-487C-BDAD-23C0B23FD662@apple.com>
To: HTML Accessibility Task Force <public-html-a11y@w3.org>

On Feb 24, 2011, at 12:37 , Philip Jägenstedt wrote:

> On Thu, 24 Feb 2011 20:36:40 +0100, David Singer <singer@apple.com> wrote:
>> On Feb 18, 2011, at 8:14 , Philip Jägenstedt wrote:
>>> On Thu, 17 Feb 2011 23:17:41 +0100, Silvia Pfeiffer <silviapfeiffer1@gmail.com> wrote:
>>>> Note that I have started a page in the wiki to collect different
>>>> rendering possibilities for multitrack video:
>>>> http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Media_Rendering
>>>> My idea is that in order to understand what different display
>>>> possibilities we have for multitrack video we have to analyse what
>>>> people do now. I get the feeling that there are only a limited number
>>>> of ways in which they can be displayed and we could possibly cover
>>>> that with CSS. We also have to consider that we don't always have all
>>>> the real estate of a Web page available to put multiple videos next to
>>>> each other, because when the video goes full-screen it is no different
>>>> to a TV display. So, getting inspiration from existing ways in which
>>>> multiple video tracks are displayed should be a good idea. Please help
>>>> with your images.
>>>> If you want to contribute images but cannot upload there directly,
>>>> feel free to email me the image and I will upload it for you.
>>> Thanks for collecting these, Silvia.
>>> Looking through the list, it's clear that all of these have a non-trivial layout of the multiple video tracks.
>>> For example, Mlbtv_02.jpg is a baseball video with plenty of overlayed information together with the extra video track. The extra video track has a special border that fits with the rest of the presentation.
>>> Transhud.jpg also has special UI around the overlayed video track, and it appears as though the many overlayed video tracks in Winclip.jpg has at least a thin black border.
>>> The conclusion I draw from this is that the effects "people" want are only really feasible with multiple <video> elements that are positioned and styled with CSS. In other words, for multi-track video, we need only really consider the technical solutions that link together several sibling <video> elements.
>> I sort of agree.  I think.  I think that when there are visual elements in the markup, then HTML and CSS should be used to position and style them.  I am not sure I agree that that means that they all have to be <video> elements.  Why can't HTML+CSS handling styling and positioning of <tracks> within the <video> as well as the overall <video> element itself?
> I suppose it's not strictly necessary to have multiple <video> elements, it just seems like a mostly straightforward solution. CSS extensions could handle positioning of tracks *within* a single <video> element, but as soon as you want to have videos that are only partially overlapping, have borders or are just at separate places in the page layout, that approach is quite limiting.

Agreed.  If HTML+CSS restricts the <track> to be within the rectangle assigned to the <video> that includes them, because the <track> is a sub-element of <video>, then that is rather limiting. Perhaps not worryingly so, but a limit.

I am fearful of designing a race car (general multi-part synchronized multimedia laid out all over the page) when what we really need are walking directions to the corner store, that's all.

David Singer
Multimedia and Software Standards, Apple Inc.
Received on Thursday, 24 February 2011 23:12:35 UTC

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