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

From: Philip Jägenstedt <philipj@opera.com>
Date: Sat, 19 Feb 2011 11:09:12 +0100
To: public-html@w3.org
Message-ID: <op.vq5ahi1esr6mfa@nog>
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.

Are there any other approaches people have in mind?

-- 
Philip Jägenstedt
Core Developer
Opera Software
Received on Saturday, 19 February 2011 10:09:48 GMT

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