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: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Sat, 4 Dec 2010 13:56:49 +1100
Message-ID: <AANLkTin5eWF3gzY_vH0CFKE7GoGd7vutsfAyqvVMMg_=@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>
This on is actually enforced by the way in which the poster is
presented. There is no possibility for the user to percieve the poster
as a separate element and independent of the video, because the poster
*is* the video. If the poster does not represent the video's content,
then the user has been deceived (on purpose) and the same deception
needs to be given to the vision-impaired user: the summary needs to be
similarly deceiving. Only the actual playback of the video - and the
associated audio description - will remove that deception.

Silvia.


On Sat, Dec 4, 2010 at 1:48 PM, John Foliot <jfoliot@stanford.edu> wrote:
> Sure, but how do you enforce that intent? HTML 4 mandated all images have alt text, and 10 years later HTML5 wants to make @alt optional because nobody followed the intent. What it should be, and what authors are going to do are two very seperate things, and we can't change that, so instead we must account for it.
>
> JF
> sent from my mobile
>
> Silvia Pfeiffer <silviapfeiffer1@gmail.com> wrote:
>
>>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
>>summary?
>>
>>
>>Silvia.
>>
>>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 02:57:44 GMT

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