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Re: Tech Discussions on the Multitrack Media (issue-152)

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Sun, 20 Feb 2011 10:42:51 +1100
Message-ID: <AANLkTi=mr2uxuP2Pt+Q4K8qwVhf768Z0Y=eckDtuRQo6@mail.gmail.com>
To: Philip Jägenstedt <philipj@opera.com>
Cc: public-html@w3.org
On Sat, Feb 19, 2011 at 9:09 PM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Fri, 18 Feb 2011 22:41:53 +0100, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
>> On 19/02/2011, at 3:31 AM, Philip Jägenstedt <philipj@opera.com> wrote:
>>> On Fri, 18 Feb 2011 17:08:28 +0100, Mark Watson <watsonm@netflix.com>
>>> wrote:
>>>> On Feb 18, 2011, at 2:08 AM, Philip Jägenstedt wrote:
>>>>> On Thu, 17 Feb 2011 18:43:49 +0100, Mark Watson <watsonm@netflix.com>
>>>>> wrote:
>>>>>> On Feb 17, 2011, at 7:17 AM, Philip Jägenstedt wrote:
>>>>>>> On Wed, 16 Feb 2011 18:47:22 +0100, Mark Watson <watsonm@netflix.com>
>>>>>>> wrote:
>>>>>>>> On Feb 16, 2011, at 12:02 AM, Philip Jägenstedt wrote:
>>>>>>>>> On Wed, 16 Feb 2011 03:31:47 +0100, Silvia Pfeiffer
>>>>>>>>> <silviapfeiffer1@gmail.com> wrote:
>>>>>>>>>> On Wed, Feb 16, 2011 at 12:08 PM, Jonas Sicking <jonas@sicking.cc>
>>>>>>>>>> wrote:
>>>>>>>>>>> On Tue, Feb 15, 2011 at 4:19 PM, Silvia Pfeiffer
>>>>>>>>>>> <silviapfeiffer1@gmail.com> wrote:
>>>>>>>>>>>> On Wed, Feb 16, 2011 at 5:36 AM, Mark Watson
>>>>>>>>>>>> <watsonm@netflix.com>
>>>>>>>>>>>> wrote:
>>>>>>>>>>>>> Hi Philip,
>>>>>>>>>>>>> Just a quick note that the "alternative" vs "additional"
>>>>>>>>>>>>> distinction
>>>>>>>>>>>>> is not always completely clear. Video with different camera
>>>>>>>>>>>>> angles
>>>>>>>>>>>>> (gimmiky or not) could be considered as an alternative, or
>>>>>>>>>>>>> could
>>>>>>>>>>>>> be
>>>>>>>>>>>>> rendered as picture-in-picture, or multiple thumbnail videos
>>>>>>>>>>>>> could
>>>>>>>>>>>>> show beside the main video (some sports sites already do this
>>>>>>>>>>>>> kind
>>>>>>>>>>>>> of
>>>>>>>>>>>>> thing).
>>>>>>>>> Sure, but all of those modes should be achieved by the author
>>>>>>>>> making
>>>>>>>>> it
>>>>>>>>> happen with CSS. At the risk of making a strawman argument, I
>>>>>>>>> honestly
>>>>>>>>> can't see browsers allowing the user to change the rendering of the
>>>>>>>>> page
>>>>>>>>> to achieve PiP or something like that when the author hasn't
>>>>>>>>> provided
>>>>>>>>> for
>>>>>>>>> it, messing with the layout like that seems both weird and unlikely
>>>>>>>>> to
>>>>>>>>> be
>>>>>>>>> useful. Of course we can have User JavaScript and User CSS to do
>>>>>>>>> that
>>>>>>>>> kind
>>>>>>>>> of thing, though.
>>>>>>>> I was assuming that the "author" of the content - who labels the
>>>>>>>> tracks
>>>>>>>> - might not be the same as the "author" of the webpage that is
>>>>>>>> rendering
>>>>>>>> the content. So the first author should not assume that (say)
>>>>>>>> multiple
>>>>>>>> views are alternatives, because some webpages might be able to view
>>>>>>>> them
>>>>>>>> both as PIP.
>>>>>>> Since the tracks are labeled using the attribute of the <track>
>>>>>>> attribute,
>>>>>>> it will be the page author that has to do the work to support some
>>>>>>> specific video display, be that PiP, overlay or something else.
>>>>>> That would be the case for track objects created as a result of
>>>>>> <track>
>>>>>> elements, but what about in-band tracks ? The page author does the
>>>>>> work
>>>>>> for PIP etc., of course, but the media author should not assume that
>>>>>> such capabilities are or are not available on the pages where their
>>>>>> media might be used: they should just label the tracks and let the
>>>>>> page
>>>>>> to whatever it is capable of.
>>>>> I don't think we should spend much time making extra in-band video
>>>>> tracks
>>>>> work more than barely, if at all, since the extra bandwidth needed to
>>>>> have
>>>>> multiple in-band video tracks makes it quite unlikely the feature would
>>>>> be
>>>>> used to any greater extent.
>>>> A track declared within an adaptive streaming manifest (e.g. a DASH
>>>> manifest or take-your-pick of various proprietary adaptive streaming
>>>> solutions) would be an in-band track but would only be fetched when actually
>>>> needed.
>>> Good point.
>>>>> If they should work at all, my position is that the only thing you
>>>>> should
>>>>> be able to do with in-band video tracks is switch between them, in
>>>>> other
>>>>> words what I've called alternative tracks. Either having some kind of
>>>>> layout information in the file itself or having HTML markup to target
>>>>> individual tracks of the same resource seems like unjustified
>>>>> complexity
>>>>> and spec/implementation effort not very well spent.
>>>> I think people do imagine that adaptive streaming manifests would
>>>> declare all the tracks needed for a presentation - including sign language
>>>> tracks that are additional rather than alternative. Such manifests have to
>>>> be useful in environments other than HTML and so need to included
>>>> everything. I don't think we should ask people to re-author them in HTML for
>>>> use in HTML environments.
>>> I quite disagree, designing something to work both in browsers and
>>> non-browsers means that we can't make good use of whatever existing
>>> capabilities browsers already have. In this case, I think we should rely on
>>> CSS and only CSS to achieve the desired rendering of multitrack video. Any
>>> default rendering we could provide is unlikely to fit well enough in with
>>> the overall design of the page that people will want to use it.
>>> Some samples Silvia collected in
>>> <http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Media_Rendering>
>>> demonstrate quite clearly IMO the variety of styles we can expect to see.
>>>> I guess what I am saying is that Option (1) in the wiki write-up should
>>>> be supported in order to provide support for adaptive streaming. The
>>>> questions are:
>>>> (1) whether this should be the only way to declare such
>>>> additional/alternative tracks or whether an HTML markup way is also required
>>>> (and I think that it is)
>>> I don't see how this approach could give us the flexibility in styling
>>> that is necessary. How do you envisage getting a visual end result similar
>>> to <http://www.w3.org/WAI/PF/HTML/wiki/File:Transhud.jpg> (note the fancy
>>> borders around the overlayed video) using a manifest approach?
>> The exercise isn't really finished yet. What I am trying to figure out is
>> whether there are common patterns. Of course we need to also allow for the
>> author to change and adapt the styling for their site. But I believe we also
>> need a default display mechanism just like the controls. That should not be
>> fancy.
>> I think it is early to draw conclusions, but we seem to see two
>> fundamentally different layouts: pip (picture-in-picture) and side-by-side.
>> The default should be without any fancy borders, just thrown either on top
>> of the main video or tiled. Either should have a single control. That's all
>> I can tell from preliminary looks.
> Of course we should continue looking into this, but at this point I can't
> see good solutions for default rendering.
> Picture-in-picure: If the page hasn't provided for it, then default
> rendering would be limited to a box within the main video's content box,
> without borders or other styling. At best it could be draggable within the
> video content box, but that would interfere with drag-and-drop and such, so
> I'm not sure.
> Side-by-side: If the page hasn't provided for it, the best we could do is to
> tile multiple videos inside the same <video> element, growing the size of it
> unless the size is restricted by CSS. If the videos are of different sizes
> things become messy. No borders or padding to separate the videos.
> What it boils down to is how we imagine styling should work. I think that
> the kind of default rendering I have outlined above is not good enough to
> spend time on. Conversely, improving on it would require CSS extensions to
> achieve things that are already trivially possible if the author uses
> multiple <video> elements, styling them with plain CSS.

There is no question that a DOM API needs to be available for the
styling. I am not sure which markup approach is most appropriate for
this, so I'm not going to discuss this here.

However, I am concerned if we say that CSS and JavaScript are the only
way to get access to and display the additional tracks. I am mostly
concerned because it creates a barrier towards broad uptake of
multitrack video. A barrier that may inhibit many people from making
use of it. A barrier that may stop people in particular from
publishing audio descriptions and sign language tracks even if they
have them available, simply because it's too difficult to publish them
if you have to write your own JavaScript and CSS code to display them.
I think we absolutely should provide a default display, even if it is
crude and not pretty (most default player controls of browsers aren't
pretty and yet lots of content is being published without custom

Another reason for having a default display is when you go
full-screen. It would be hard if not impossible to create the layouts
for fullscreen display for multitrack video without the browser taking
care of it.

To make it simple, I think we don't need fancy borders around videos
that are shown picture-in-picture. The sheer matter that they are
moving pictures makes the eye recognize that there is a different
video happening inside. Maybe,it could just have a single pixel black
and a single pixel white border - that would probably satisfy all
contrast needs. But definitely nothing fancy.

The idea of making the pip videos movable is a good one. I'm sure
conflicts with other drag and dop / mouse operations can be resolved.
It probably just need to sit at a certain zindex level and then people
can style around that.

I have been thinking lots about side-by-side video and how to display them.

If they are separate boxes on the Web page, that makes it difficult to
have a single @controls to navigate across them. I think the
complexity of multiple @controls may be too hard to deal with. Thus,
right now I tend towards the idea that they should all be displayed in
a single viewport. If a side-by-side display is requested and we have
two video tracks, then they would sit next to each other with
letterboxing on top and bottom. That would also provide space for
captions to be moved into.

When we have side-by-side and 3 video tracks, I would think there's
two next to each other, one centered below them and pillarboxing
around it.

When we have side-by-side and 4 tracks, they would get tiled, etc.

If the sizes don't match, appropriate letter- and pillarboxing would be used.

Scaling would need to be within the viewport given for the main video
- either through CSS or through the width/height of the main video
track. This is the base viewport size and within that the tiling would
happen by subdividing the viewport size into equal size rows and
columns and adequately letter- / pillarboxing. That should also allow
to reuse most of the scaling code that is already in use for the
single-track videos.

If people want more fancy displays than that, the can implement them
with JavaScript and CSS. Then there could also be spaces defined
outside the viewport into which they can be rendered but fall back to
the viewport-only display when you go fullscreen.

Received on Saturday, 19 February 2011 23:43:44 UTC

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