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Re: ACTION-187: extensibility and parsing

From: Philip Jägenstedt <philipj@opera.com>
Date: Mon, 04 Oct 2010 09:34:09 -0400
To: "Yves Lafon" <ylafon@w3.org>
Cc: "Media Fragment" <public-media-fragment@w3.org>
Message-ID: <op.vj1zy7y4sr6mfa@philip-pc>
On Mon, 04 Oct 2010 08:08:21 -0400, Yves Lafon <ylafon@w3.org> wrote:

> On Wed, 22 Sep 2010, Philip Jägenstedt wrote:
>
>> By extensibility I am not primarily talking about 3rd parties extending  
>> MF, but about our own possibilities of updating the spec after MF 1.0.  
>> For the purpose of discussion, assume that we want to add a dimension  
>> for filtering the audio, e.g., freq=300,3000 to keep only the part of  
>> the audio that corresponds (approximately) to human voice  
>> (300Hz-3000Hz).
>
> Well, even in our case we have to be very careful in the way we do  
> extensions, take for example the 'ref' proposal that was sent to the  
> list to define a region (using a polygon), it is in the spatial  
> dimension so in conflict with xywh. What does  
> http://www.example.com/foo#xywh=10,20,34,40&ref=http://example.com/shape  
> mean? Union? Intersection? fallback to xwyh if ref can't be processed?
>
> So just stating that we can allow every possible extension in the  
> grammar or in the parsing rules is far from being enough, we need to  
> have a high bar to avoid such conflicts.

This is an easy problem to solve. Implementation of MF 1.0 will ignore  
ref, only applying xywh. Implementations that understand MF-with-ref will  
do whatever that spec says. However, it would of course be best if ref  
doesn't change the semantics of xywh, as the fallback in MF 1.0 UAs would  
then be better.

-- 
Philip Jägenstedt
Core Developer
Opera Software
Received on Monday, 4 October 2010 13:35:19 GMT

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