W3C home > Mailing lists > Public > public-html@w3.org > September 2008

Re: Acessibility of <audio> and <video>

From: Lachlan Hunt <lachlan.hunt@lachy.id.au>
Date: Mon, 01 Sep 2008 23:36:15 +0200
Message-ID: <48BC604F.1010809@lachy.id.au>
To: Leif Halvard Silli <lhs@malform.no>
Cc: 'HTML WG' <public-html@w3.org>

Leif Halvard Silli wrote:
> Justin James 2008-09-01 19.42:
>> I can imagine the furor if we also applied this logic to
>> images, by saying, "if you want accessible images, use a format
>> that natively supports metadata of alternate text, or put a
>> subtitle/caption/legend/etc. in your image."

No. Unlike video, images have no way embedding accessibility features 
within them, and their meaning is very often depending on the context. 
However, videos do have various ways of including native accessibility 
features, such as subtitles/captions or audio descriptions.

> Add to that that movie formats are *very* often used for displaying 
> photos.

Could you elaborate on what you mean, provide some sort of evidence to 
support this claim, and also explain why it's relevant?

> Plus the fact the <video> elment itself has a poster image to be 
> displayed before the video is started.

I'm not sure why that is relevant.  The poster frame can be thought of 
as being more like an icon representing the video.  It's the content of 
the video that is important

> instead allow textuall fallback <element>inside the element</>, then 
> that would be better.

OK, let's look at the various kind of alternatives that could be 
potentially provided for people who either can't watch or don't want to 
watch the video.

* Transcript of spoken content.
* Textual descriptions of relavant non-spoken content.
   e.g. descriptions of significant actions or sounds in the video.
* Still images illustrating significant moments from the video.
   e.g. images of presentation slides, if the video was of someone giving
   a presentation.
* A link to download the video, possibly in alternative formats, to
   watch in an external media player, perhaps in several formats.
* Video embedded in the page using an alternative method
   e.g. Flash, the Cortado Theora applet, or whatever

Any or all of those could be provided and all of them would be suitable 
for people in the following categories:

1. People using browsers that don't support <video>
2. People using browsers that do support video, but don't support the
    codecs used.
3. People who can't see the video well (blind or visually impaired)
4. People who can't hear the video well (hearing impared or no
    headphones/speakers available)
5. People who want to search the content of the video
    e.g. Instead of seeking through the video to find the information
    they want, just look through the transcript, from which they can also
    copy quotes if they want.

Given that the alternative content is useful to so many people, 
regardless of physical disability or technological limitations, it makes 
  sense for it to be provided in a way that makes it available to 
everyone.  This is one reason why hiding alternative content away within 
the video element is not helpful because it only makes it readily 
available to a small subset of those people who might want or need it.

Another reason to consider is that we know very well what authors do 
when they are encouraged to hide alternative content specifically for 
accessibility within elements.  For example:

<noframes>Your browser does not support frames, Please upgrade to
Netscape 4</noframes>

<noscript>Sorry, your browser doesn't support javascript.</noscript>

<object ...>Please install flash</object>

It might work ok for <video> during the transitional period when not all
browsers implement it, since authors will gain practical benefits by
including alternative embedding mechanisms within the video element. e.g.

<video src="movie"><object data="movie"></object></video>
<p><a href="movie">Download movie</a>
    <a href="transcript">Read transcript</a> ...

But, in the long term, after browsers with native video support are more
widely used, we'll likely start seeing people leaving the video element
empty or including useless messages, and accessibility loses.  Whereas 
by encouraging people to use visible alternative content,
everybody wins.

Lachlan Hunt - Opera Software
Received on Monday, 1 September 2008 21:36:56 UTC

This archive was generated by hypermail 2.3.1 : Thursday, 29 October 2015 10:15:37 UTC