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Working Group Decision on 142 poster-alt

From: Sam Ruby <rubys@intertwingly.net>
Date: Tue, 29 Mar 2011 10:59:44 -0400
Message-ID: <4D91F3E0.4070004@intertwingly.net>
To: HTML WG <public-html@w3.org>
The decision follows.  The chairs made an effort to explicitly address
all arguments presented in the Change Proposals on this topic in
addition to arguments posted as objections in the poll.

*** Question before the Working Group ***

There is a basic disagreement in the group as to whether or not the
HTML5 specification should require or even make available an
alternative text description for the placeholder image for the video
element.  Additionally, there is a disagreement over the name of the
attribute or element to be used for the placeholder image itself. The
result was an issue, two change proposals, and a straw poll for
objections:

http://www.w3.org/html/wg/tracker/issues/142
http://www.w3.org/html/wg/wiki/ChangeProposals/NoPosterAlt
http://www.w3.org/html/wg/wiki/ChangeProposals/PosterElement
http://www.w3.org/2002/09/wbs/40318/issue-142-objection-poll/results

== Uncontested observations:

* The removal of the @poster attribute will cause current experimental
   examples of <video> in the wild to break once user-agents implement
   this change.

* Element syntax is slightly more verbose than an attribute syntax in
   this case.

* Short text alternatives for the video itself are important.

* Authors can use any image as the poster frame.

None of these were decisive.  There were people who supported either of
these proposals even after taking these facts into consideration.  The
fact that they were acknowledged up front was appreciated.

=== Need for text alternatives for placeholder image

As we generally do, we start with the positive effects listed for each
proposal.  In this case, the positive effects stated for the "No Poster
Alt" Change Proposal were not found to be applicable and therefore not
considered (see section below for details).  Taking the positive
effects listed in the "Introduce a new <firstframe> element" Change
Proposal, we extract the following objections (paraphrased) to the "No
Poster Alt" proposal: that it is does not allow for accessibility or
internationalization requirements, and that the description is
ambiguous.

The "Introduce a new <firstframe> element" Change Proposal also
provides a concrete example where it is felt that such text would be
necessary.

At this point we only have objections to the "No Poster Alt" Change
Proposal, so we turn to examine objections to the "Introduce a new
<firstframe> element" to see if we find a stronger one.  Each of the
following are quotes from the survey:

   Given that sighted users won't know (or, if they do, care) that
   they're looking at the poster image, it would be confusing and
   inconsistent to have a short text alternative specifically for the
   poster image for non-sighted users.

This is an opinion.  Given that there was a concrete counter-example
presented, this opinion was not given much weight.

   I strongly object to describing the poster frame separately from the
   video to AT users. This distinction is not made for sighted users,
   who have no way of knowing if what they are seeing is the first frame
   of a video or a poster frame. The poster frame is "intended to be a
   representative frame of the video" and as such, the description of
   the video should also be a suitable description of the poster frame.
   If the poster frames brings attention to any specific aspect of the
   video, it would be appropriate for the video's description to also
   stress that aspect. Making the suggested disctinction would encourage
   inappropriate use of the poster frame.

Again, we have a concrete counter-example and no evidence that it is
"inappropriate".

   it seems highly unlikely that people who use the poster incorrectly
   (to include content that is not representative of the video resource
   itself) would be aware enough to make the effort of making that
   inappropriate use accessible.

Again, we have a concrete counter-example and no reason to believe it
is "incorrect".

   The proposal confuses poster frames with movie posters. It is not
   purpose of this attribute to serve as a movie poster, and I have not
   seen any indication of this happening in practice.

No explanation is provided as to why it would be inappropriate or
incorrect for an attribute which is named "poster" which is intended to
convey an image indicative of the content to actually be an image of a
poster.

   The proposal is mainly based on concern that authors *could* use
   image that contains unique and valuable information about the video.
   However, this does not happen in practice.

Again, we have a concrete counter-example.

   That <video> does not have a (dedicated) short text alternative is
   part of the point. Having a dedicated short text alternative for the
   poster frame but not for the video itself is extremeley backwards.

This is an opinion.  Given that there was a concrete counter-example
presented, this opinion was not given much weight.

   In my experience most videos don't have carefully chosen poster
   frames that are good description of the video, and many videos have
   accompanying description which makes description of poster frame
   unnecessary.

   Description of only a single frame  which sometimes is not even
   chosen by the video author  can be misleading about video's content.

   Poster frames on sites like YouTube or Vimeo are just one of the
   frames of the video. These frames are not specially crafted images
   that would be a good proxy for the entire video contents.

These were three separate comments, but taken together we find that we
have concrete counter-examples to the "firstframe element MUST contain
alt" normative requirement in the "Introduce a new <firstframe>
element" Proposal. Looking at that change proposal, we find no
rationale for this requirement.

There is also an objection to naming this attribute "first frame", but
that objection is a "necessary consequence" of the objection that this
is already implemented by browsers and used by web pages.

Finally, there is this:

   I object to introducing a <firstframe> void element that is likely to
   appear before the <source> elements. In all browsers that do not
   implemented support for <firstframe>, any following <source> elements
   would become child elements of <firstframe> and thus would not be
   considered in the resource selection algorithm. In effect, that video
   would be completely broken in those browsers. (Yes, this is also a
   problem with <track> and introducing new void elements in general.)

Looking deeper into this it turns out that the "Introduce a new
<firstframe> element" Change Proposal is internally inconsistent.  It
provides spec text that describes an element with a value of a url, but
then provides examples where the value is placed in a src attribute.

At this point, we have strong objections to the requirement that the
firstframe MUST contain alt, and an inconsistent Change Proposal.

For completeness, we evaluate the objections to the "No Poster Alt"
proposal.  Along with responses to objections already dealt with, a
discussion on what would be the best name, as well as the following
statements which reinforce the arguments in the original change
proposal:

   HTML5 should have a mechanism to provide that indication to people
   with disabilities. Currently it does not. <firstframe> provides that
   possibility.

   the firstframe image can have value in itself

These arguments are strong, but do not address the strong arguments
against making this indication mandatory.  The evidence for the need to
provide a separate textual description of the firstframe is indirect
(in the form of an example poster that somebody *might* use) vs direct
(a list of actual sites that deploy videos today and an explanation as
to why a requirement to make providing an alternate text description
mandatory would be inappropriate in those cases).  Additionally there
is the problem that the "Introduce a new <firstframe> element" Change
Proposal is internally inconsistent, and that it introduces a
non-backwards compatible change which affects existing content and
implementations without providing a migration plan.

*** Decision of the Working Group ***

Therefore, the HTML Working Group hereby adopts the "No Poster Alt"
Proposal for ISSUE-142.  Of the Change Proposals before us, this one
has drawn the weaker objections.

== Next Steps ==

Bug 10642 is to be CLOSED and marked as WGDecision.  Additionally,
ISSUE-142 is to be marked as CLOSED.

Since the prevailing Change Proposal does not call for a spec change,
no further action is required.

== Appealing this Decision ==

If anyone strongly disagrees with the content of the decision and would
like to raise a Formal Objection, they may do so at this time. Formal
Objections are reviewed by the Director in consultation with the Team.
Ordinarily, Formal Objections are only reviewed as part of a transition
request.

== Revisiting this Issue ==

This issue can be reopened if new information come up. Examples of
possible relevant new information include:

* Identification of use cases that specifically require a different
   description for the placeholder/poster/firstframe image than for the
   video itself.  These use cases would need to cover every normative
   requirement identified in any Change Proposal which might accompany
   the request to reopen the issue based on new information.  Ideally
   evidence for these use cases would be provided in the form of real
   world deployments of videos on the web.

=== Arguments not considered:

   "Discussion can move on"

Not helpful in determining the proposal that draws the weakest
objections.

   "Adding a short text alternative for the placeholder/poster image
   (which I object to) does not require changing this part of the
   syntax."

We only consider proposals which actually are put forward.
Received on Tuesday, 29 March 2011 15:00:16 GMT

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