W3C home > Mailing lists > Public > public-html@w3.org > February 2011

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

From: Mark Watson <watsonm@netflix.com>
Date: Fri, 18 Feb 2011 09:44:14 -0800
To: Philip Jägenstedt <philipj@opera.com>
CC: "public-html@w3.org" <public-html@w3.org>
Message-ID: <C3386E03-04E1-44E5-A83B-3ED8AECCCA0A@netflix.com>

On Feb 18, 2011, at 8:31 AM, Philip Jägenstedt 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.

I don't disagree with using CSS to achieve the desired rendering in a HTML environment, but I don't understand why that conflicts with what I wrote above ?

> 
> 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?

Again, not sure I understand the problem.

It seems important that with adaptive streaming all the tracks are declared together in the manifest and so the transport of those can be handled by the player in an HTML-independent way. The same adaptive streaming player software components can be reused across different environments. The transport of the different tracks interacts, so they should not be handled independently.

If I understand correctly, you are saying that in an HTML environment you would like the full power of HTML+CSS to be available to control the presentation of the tracks - I completely agree (otherwise why are you using an HTML environment at all?). So some means of applying CSS styling to in-band tracks is required. That seems to be the case both for in-band tracks in a single file and those described in a manifest.

That means a single manifest could be used in both HTML and non-HTML environments and in the HTML environment you would have the flexibility to style the tracks with CSS if you chose to.

I'd like to avoid having to re-invent all the transport-related aspects of adaptive streaming manifests at the HTML level.

> 
>> (2) what should that markup be
>> (3) how to define the API for discovering and manipulating these tracks  
>> in a way that is common for in-band (from a file or from an adaptive  
>> streaming manifest) and explicitly marked up tracks.
> 
> From a markup and API perspective a multitrack manifest file would be  
> treated the same as a multitrack WebM file, right?

>From an API perspective, certainly.

I don't know what has been discussed for markup of multi-track WebM files: do you expect the multiple tracks to be exposed in HTML with explicit <track> elements, or do they just appear in the API when the file is loaded ? If the latter, then yes, I would see a multitrack manifest file as no different from a multitrack media file (except perhaps that the manifest could possibly be loaded earlier).

...Mark

> 
> -- 
> Philip Jägenstedt
> Core Developer
> Opera Software
> 
> 
Received on Friday, 18 February 2011 17:48:27 UTC

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