Re: Track kinds

On Sat, May 7, 2011 at 5:22 AM, Mark Watson <> wrote:
> All,
> I updated the wiki page
> at based on our meeting on
> Wednesday.
> The three proposed additional kinds are: captions, subtitles and clearaudio.
> Please everyone check the definitions on the page.

Looks good to me.

> The next decision is
> whether to re-open the previous "kinds" bug or create a new one.

Two existing bugs relate to kind:
This one relates to @kind on text tracks mostly, so is probably not relevant.
This one relates specifically to getKind().

I would propose to just add our request for these three additional
strings to that latter bug.

> I also have a procedural question: do we consider that we have received the
> liaison from 3GPP (mentioned on the above page) ? Are we going to answer it
> ?

There should be an email by a 3GPP member with all the relevant
requests to the WG list. I haven't seen one such. Unless that arrives,
there is nothing to reply to.

> One question they ask is whether we will define a URN to identify the
> space of kind values defined by W3C. One advantage of doing that is that
> these kinds are then immediately supported in 3GPP and MPEG adaptive
> streaming manifests, which means that there *is* a media container
> supporting those kinds (perhaps addressing one of the editor's concerns
> about new kind values).

I don't think HTML needs these values as anything else but short
strings that we now have.

If 3GPP and MPEG need them as URNs - and they probably have a swag
more that they have proposed and will use - it makes a lot more sense
to me for them to define these themselves. Some of the kinds that
media containers will expose may just end up creating getLabel() text
rather than be exposed in getKind(). Ogg already seems to have a few
of those.

> Finally, we discussed the "commentary" kind here at Netflix and in the end
> we are happy to have it dealt with simply as "alternative". I do think
> though that in principle there could be other (UI-related) reasons for
> exposing a new track kind than triggering default behavior or application of
> user preferences. This is certainly the case for accessibility use-cases
> where the UI to enable/disable a particular track could usefully be tailored
> to the intended users of that track (for example, enabling/disabling tracks
> intended for the blind or those with low vision should ideally not involve
> complex visual UI elements).

OK. I think we'll cross that bridge when we get to it.


> ...Mark
> On May 3, 2011, at 10:12 PM, Silvia Pfeiffer wrote:
> I understand the problem of additive/alternative tracks, too, and have
> tried to approach it with markup before. However, I think this is
> making something that is supposedly simple much too difficult. The
> ultimate choice of active tracks has got to be left to the user. For
> this reason, I think @kind (or getKind()) should only ever expose what
> content is available in the track, but there should not be an
> automatic choice made by the browser. It's up to the user to
> activate/deactivate the correct tracks.
> Before we dive into anything more complex, we should get some
> experience with an implementation of multitrack and the roles. I don't
> think we will have much to go by for making a decision beforehand.
> Cheers,
> Silvia.
> On Wed, May 4, 2011 at 2:02 PM, Mark Watson <> wrote:
> So, if we are looking for a generic approach, where a track can have
> multiple "roles", then I think the correct logic is indeed to pick the
> fewest number of tracks which fulfill the intersection of the desired roles
> and the available roles such that no role is fulfilled more than once. You
> need a priority list of roles to drop from the desired list if that isn't
> possible (which would mean some badly authored content, but has to be dealt
> with). It may be a mouthful, but I think it would be reasonably
> straightforward to implement.
> However, I'm still not sure a generic approach is necessary. A "simpler"
> approach is to say every track has a single role. But for some applications
> (like audio descriptions) there are two distinct role values defined - an
> additive one and an alternative one. The problem is addressed at a semantic
> level - i.e. people implement support for audio descriptions - and they know
> what these are and how to handle them - rather than trying for a generic
> descriptor matching algorithm.
> Regarding Repetitive Stimulus Safe, I guess that since most content is
> unfortunately not labeled one way or the other the default assumption has to
> be up to the user themselves. i.e. that user preferences associated with
> this aspect should support required, preferred and don't care. In a really
> generic approach every role may have a status from { require, prefer, don't
> care, prefer not, require not }.
> Again, this suggests that a generic approach might be over-ambitious - who
> says some new role doesn't come along next week with a sixth user-preference
> status of "required unless role Y present" or similar ... I think maybe the
> UA needs to understand what these things are and act appropriately.
> ...Mark
> On May 3, 2011, at 11:55 AM, David Singer wrote:
> On May 2, 2011, at 16:55 , Mark Watson wrote:
> I think it's evidence that there is something to be solved.
> I'd prefer a solution where adding a track to an existing presentation
> didn't require me to change the properties of existing tracks, though, since
> there is an error waiting to happen in that case.
> Yes.  This idea made some sense when it was the tracks in a multiplex (e.g.
> MP4 file), perhaps makes sense when all the tracks are annotated in the
> markup (e.g. in HTML5 or DASH MPD) but makes much less sense when some
> tracks are in a multiplex and some are added in the markup - a track added
> in the markup might need the annotations in a multiplex changed, ugh.
> So, thinking out loud here.
> Assume the user has a set of roles that they would kinda like to experience.
>  The default is 'main, supplementary', I think, or something like.
> Now, we have a set of tracks, each of which satisfies some roles.  Let's
> ignore tracks we have discarded because they are the wrong mime type, codec,
> language, etc., and focus just on this selection mechanism.  What is the
> right simple way to get the set of tracks?
> It's easy to 'go overboard' and treat this as a very general problem of
> finding the minimal set of tracks that will span a set of design roles.  I
> don't think anyone will author *for the same language*
> track - main
> track - captions
> track - main +  captions
> so an algorithm designed to pick only (3) instead of (1 + 2) for the
> main+captions desiring user is probably overkill.
> 'enable the tracks whose roles are a subset of the desired roles, and
> disable the rest' may be too simple, unless tracks are ordered from the
> most-labelled to the least-labelled.
> So, audio-description replacing the main audio:
> track - main description
> track - main
> Audio description adding to the main audio
> track - main
> track - description
> The same works for all the adaptations that might require re-authoring or
> might be achievable with an additional track (captions, burned in or
> separate, for example).
> Where this fails is when the 'base content' is good enough for both the
> plain user and the user who desires more roles.  The obvious case here (Mark
> will laugh) is repetitive-stimulus-safeness;  we have to assume unlabelled
> content is unsafe, but much content is naturally safe and can be labelled as
> such.
> David Singer
> Multimedia and Software Standards, Apple Inc.

Received on Friday, 6 May 2011 21:19:16 UTC