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

RE: Video Poster image (was RE: DRAFT analysis of fallback mechanisms for embedded content ACTION-66)

From: John Foliot <jfoliot@stanford.edu>
Date: Fri, 3 Dec 2010 13:35:52 -0800 (PST)
To: "'Maciej Stachowiak'" <mjs@apple.com>
Cc: "'Martin Kliehm'" <martin.kliehm@namics.com>, "'Silvia Pfeiffer'" <silviapfeiffer1@gmail.com>, "'HTML Accessibility Task Force'" <public-html-a11y@w3.org>
Message-ID: <00ea01cb9332$0f1da500$2d58ef00$@edu>
Maciej Stachowiak wrote:
> Why is that better than including that text in the video summary?
> It seems like the poster frame and your suggested label/summary text
> both serve the same purpose - helping the user decide if they want to
> play the video.

This may not always be true.

> They are auxiliary content. Describing the poster frame
> seems like an overly literal-minded approach to equivalent content.

I have repeatedly suggested (and offered as example) image files that
would serve as poster frames that contain content that is not related to a
video. This can be doubly problematic when the image contains text (a
likely probability). It is for this reasons that the image requires the
ability to have an alt value. I again urge all to review

> What is needed is a summary of the video that equally allows non-
> sighted users to decide if they want to play it, just as the poster
> frame (whether explicit or built-in) does for sighted users. 

This presumes that the poster frame will always be chosen to elicit that
call-to-action. I am trying to explain that this may not always be the
case - that the image chosen by any given author could serve an
alternative purpose (whether branding, informational, or other) that is
conceptually unrelated to a specific video, but meets other author

I agree that the video should have a summary, and even leave open the door
that it could be explicit (@summary) or 'relative' (aria-describedby) -
where here the Summary would appear as text on the page for both sighted
and non-sighted users.

However that summary does not serve as the @alt value for the image being
used - it can't, as then you are mixing oranges and apples. My video is
not about "Stanford University - this video is closed captioned" it is
about (whatever it is about). I have no disagreement that the author
*could* add this information into a summary, but I must also concede that
they might not, or that the text example I am using here is an imperfect
example (as another example - some 'gentlemen's sites' might contain
videos of, shall we say, a 'couple', where the first frame is the legally
required assertion that the 'models' in the video are of legal age and
that the record of notice is located at some law office address in
Southern California; and yes, blind and low-vision users visit websites
like that too); the point is there exists a real probability that:

	a) An image used as a poster frame could be completely unrelated
to the video it proceeds, thus not conceptually part of that video and not
covered by a video summary (The same image could be reused for multiple

	b) A poster image could contain text not located elsewhere on the
page, text that is not really part of the summarization of the video, and
so a means to convey that information to the non-sighted must exist.

Maciej, I have tussled with this a fair bit and have even done my own
sanity check to ensure that I am not misguided here, and the overwhelming
consensus I get, from both accessibility specialists as well as blind
users themselves, is that this is not off-track: we are dealing with 2
discrete assets - a video and an image - and they both require the ability
to have textual fallbacks. They may be conceptually closely related, but
they can equally be conceptually unrelated, and that is the overarching
use-case, when they are conceptually unrelated.

The change Proposal I am working on now approaches the issue from the fact
that we have 2 assets, a video and an image (<poster>), and that textual
fallback for either should exist independent of the other. It builds on an
existing pattern (the <video> element contains children elements, <src>,
<track>, and so <poster>) which also has an eye/thought towards how to
'teach' authors about this - treating both assets as the discrete assets
they are is an easy concept that most seem to grasp - at least when I
discuss this with mainstream authors around here. It might feel like an
overly literal-minded approach to engineers such as yourself, but when
trying to teach non-professionals literal is not always a bad thing. 

Received on Friday, 3 December 2010 21:36:26 UTC

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