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

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Sat, 4 Dec 2010 13:04:31 +1100
Message-ID: <AANLkTikhLF0QfOSDFeERYqK0yYLMwUKw61jObSct74Da@mail.gmail.com>
To: John Foliot <jfoliot@stanford.edu>
Cc: Maciej Stachowiak <mjs@apple.com>, Martin Kliehm <martin.kliehm@namics.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Note that the HTML5 specification clearly states:
"The image given by the poster attribute, the poster frame, is
intended to be a representative frame of the video (typically one of
the first non-blank frames) that gives the user an idea of what the
video is like."

The poster is clearly not a separate object to the video and should
not be dealt with as a separate thing.

To me the question here is rather: do we need a short text alternative
for the video (which would then contain the description of what's on
the thumbnail - no matter if it's a poster or first video frame)? And
do we need this in addition to a long text alternative, which is the


On Sat, Dec 4, 2010 at 8:35 AM, John Foliot <jfoliot@stanford.edu> wrote:
> 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
> http://dev.w3.org/html5/alt-techniques/#replacement
>> 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
> needs/goals.
> 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
> videos)
>        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.
> JF
Received on Saturday, 4 December 2010 02:05:27 UTC

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