Re: [media] how to support extended text descriptions

Hi Janina,

You take objection to a short example that was placed in brackets as a
potential use case for a broader audience than just vision-impaired
users. I'm sorry that that got you side-tracked on the real issue that
this email is trying to solve. I'm happy to remove that half sentence
in brackets if that gets us focused on the issue at hand, which is a
technical, not a use case issue.

What I tried to describe was a means for how we can solve the real use
case that you are talking about and that we included into the
accessibility requirements.

In fact, the rest of the email analyzes how we can provide extended
descriptions. We already have the markup in HTML through the text
track and the "descriptions" type. We now need to find a way in which
it can work in practice rather than just theoretically hoping it will
"just work".

I believe I've tracked the issue down to being one of the
communication between the screen reader and the Web browser. I wanted
validation of this thought process.

Please, let's not get side-tracked by a throw-away comment, but stay
focused on the real issue here: how are we technically going to solve
the extension problem.


On Sun, Jun 5, 2011 at 8:18 AM, Janina Sajka <> wrote:
> This is incorrect. If the use case language you quote below is currently in the spec docs, it is
> it dilutes and obfiscates the consensus User Requirements we created
> some months back when we created and circulated our media accessibility
> user requirements document.
> There is no accessibility use case relating to driving (a car, a train,
> or any other vehicle). Inasmuch as numerous governmental entities have
> begun criminalizing the simple acts of talking and texting on cell
> phones, the far more complex activity of interacting with web content
> seems to me only to beg the acceleration of legal interdicts.
> In any case, we don't need a made-up mainstream use case in order to legitimate
> our very real a11y use case.  Nor is our nonspeculative use case for
> extended textual descriptions specific to people who are blind. It is
> also applicable to people with low vision or people with any of a range
> of learning or cognitive disabilities,  as we explain in our User
> Requirements document:
> Recall also that we have a demonstration video, courtessy of NCAM, of an
> actual use of extended description in a MIT physics lecture.
> Furthermore, I assert our a11y use case does require support for markup,
> for many of the same reasons we need markup in support of poster. Note
> that the greater use of extended descriptions, whether recorded audio or
> textual, is likely to be educational, so that multi-lingual vocabulary
> is highly likely, as is subject-specific technical vocabulary. This
> alone is sufficient reason for ml support, imho.
> These are the requirements we need to satisfy. If that also leads to the
> enablement of a
> generalized use case, well and good. But, not every a11y solution has
> generalized application. Braille and sign language are unlikely ever to
> attain general uptake, for instance. Yet both braille and sign language
> are critically important to the people who need them
> The a11y use case is a real use case, in other words, requiring real
> solutions in HTML 5, regardless of whether it ever leads to a
> generalized application (or not).  May I suggest we focus on solving
> real needs before we indulge in fantasies about screen readers in
> vehicular instrument panels?
> Janina
> Silvia Pfeiffer writes:
>> Hi all,
>> I'm aware that we are currently focused on trying to sort out
>> hierarchical navigation, but I also want to bring the extended text
>> descriptions into the mix to make sure we understand how that can
>> work.
>> Ian and I have discussed recently how we would address this need and
>> whether there would be a requirement for extra markup.
>> I believe the below discussion is a good summary of how we envisage it
>> to work. Please provide feedback and ask questions if it anything is
>> unclear.
>> With the below described approach (which we discussed at the WHATWG),
>> there is no need for extra markup, but there is a requirement on the
>> accessibility API between a screen reader and the browser. On that API
>> we would need the possibility for the screen reader to influence how
>> the player works.
>> I suggest we need to talk to developers of browser accessibility APIs
>> and also to screen reader developers to see what they say about it and
>> whether this is technically realistic. I would encourage you to try
>> and get such information.
>> Looking forward to your comments.
>> Cheers,
>> Silvia.
>> On Tue, 24 May 2011, Silvia Pfeiffer wrote:
>> >
>> > Ian and I had a brief conversation recently where I mentioned a problem
>> > with extended text descriptions with screen readers (and worse still
>> > with braille devices) and the suggestion was that the "paused for user
>> > interaction" state of a media element may be the solution. I would like
>> > to pick this up and discuss in detail how that would work to confirm my
>> > sketchy understanding.
>> >
>> > *The use case:*
>> >
>> > In the specification for media elements we have a <track> kind of
>> > "descriptions", which are:
>> > "Textual descriptions of the video component of the media resource,
>> > intended for audio synthesis when the visual component is unavailable
>> > (e.g. because the user is interacting with the application without a
>> > screen while driving, or because the user is blind). Synthesized as a
>> > separate audio track."
>> >
>> > I'm for now assuming that the synthesis will be done through a screen
>> > reader and not through the browser itself, thus making the
>> > descriptions available to users as synthesized audio or as braille if
>> > the screen reader is set up for a braille device.
>> >
>> > The textual descriptions are provided as chunks of text with a start
>> > and a end time (so-called "cues"). The cues are processed during video
>> > playback as the video's playback time starts to fall within the time
>> > frame of the cue. Thus, it is expected the that cues are consumed
>> > during the cue's time frame and are not present any more when the end
>> > time of the cue is reached, so they don't conflict with the video's
>> > normal audio.
>> >
>> > However, on many occasions, it is not possible to consume the cue text
>> > in the given time frame. In particular not in the following
>> > situations:
>> >
>> > 1. The screen reader takes longer to read out the cue text than the
>> > cue's time frame provides for. This is particularly the case with long
>> > cue text, but also when the screen reader's reading rate is slower
>> > than what the author of the cue text expected.
>> >
>> > 2. The braille device is used for reading. Since reading braille is
>> > much slower than listening to read-out text, the cue time frame will
>> > invariably be too short.
>> >
>> > 3. The user seeked right into the middle of a cue and thus the time
>> > frame that is available for reading out the cue text is shorter than
>> > the cue author calculated with.
>> >
>> > Correct me if I'm wrong, but it seems that what we need is a way for
>> > the screen reader to pause the video element from continuing to play
>> > while the screen reader is still busy delivering the cue text. (In
>> > a11y talk: what is required is a means to deal with "extended
>> > descriptions", which extend the timeline of the video.) Once it's
>> > finished presenting, it can resume the video element's playback.
>> >
>> > IIUC, a video is "paused for user interaction" basically when the UA has
>> > decided to pause the video without the user asking to pause it (i.e. the
>> > paused attribute is false) and the pausing happened not for network
>> > buffering reasons, but for other reasons. IIUC one concrete situation
>> > where this state is used is when the UA has reached the end of the
>> > resource and is waiting for more data to come (e.g. on a live stream).
>> Ian's comment:
>> That latter state is not "paused for user interaction", it's just stalled
>> due to lack of data. The rest is accurate though.
>> > To use "paused for user interaction" for extending descriptions, we need
>> > to introduce a means for the screen reader to tell the UA to pause the
>> > video when it reaches the end of the cue and it's still busy delivering
>> > a cue's text. Then, as it finishes, it will un-pause the video to let it
>> > continue playing.
>> >
>> > To me it sounds like a feasible solution.
>> >
>> > The screen reader could even provide a user setting and a short-cut so a
>> > user can decide that they don't want this pausing to happen or that they
>> > want to move on from the current cue.
>> >
>> > Another advantage of this approach is that e.g. a deaf-blind user could
>> > hook up their braille device such that it will deliver the extended
>> > descriptions and also deliver captions through braille with such
>> > extension pausing happening. (Not sure that such a user would even want
>> > to play the video, but it would be possible.)
>> >
>> > Now, I think there is one problem though (at least as far as I can
>> > tell). Right now, IIUC, screen readers are only passive listeners on the
>> > UA. They don't influence the behaviour of the UA. The accessibility API
>> > is basically only a one-way street from the UA to the AT. I wonder if
>> > that is a major inhibitor of using this approach or whether it's easy
>> > for UAs to overcome this limitation? (Or if such a limitation even
>> > exists - I don't know enough about how AT work...).
>> >
>> > Is that an issue? Are there other issues that I have overlooked?
>> Ian's comment:
>> That seems to be entirely an implementation issue.
> --
> Janina Sajka,   Phone:  +1.443.300.2200
> Chair, Open Accessibility
> Linux Foundation      
> Chair, Protocols & Formats
> Web Accessibility Initiative
> World Wide Web Consortium (W3C)

Received on Saturday, 4 June 2011 23:16:19 UTC