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Re: [PR Media Fragment] specify how further keywords would be added

From: Jack Jansen <Jack.Jansen@cwi.nl>
Date: Sun, 22 Apr 2012 23:43:00 +0200
Cc: liam@w3.org, public-media-fragment@w3.org
Message-Id: <4E15DEDC-958B-48A9-BC20-E72ACA34A77C@cwi.nl>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>

On  22-Apr-2012, at 03:53 , Silvia Pfeiffer wrote:

>> Second, current practice for HTML user agents includes scaling of images
>> to fit a specified rectangle. One can easily envision other
>> transformations, such as those included in SVG. How would one extend the
>> notation defined in Media Fragments URI 1.0 to support a sequence of
>> transformations, and not only offset and crop? e.g. to scale
>> horizontally by 50% would it be xySwh=160,120,0.5,320,240 or should
>> implementers wishing to add such functionality use a syntax like
>> xywh=160,120,320,240,hscale=0.5 ?
> 
> The specification provides a means to include more parameters to the
> media fragment URIs as specified in the following section:
> http://www.w3.org/TR/media-frags/#general-structure
> 
> Essentially, you would create more namevalue parameters and add them with "&" .
> 
> Both your proposals are possible approaches. However, your second
> approach with introducing another parameter is likely better than the
> first one, because otherwise a new parameter would nullify an existing
> one (i.e. xySwh would nullify xywh) which is not as easy to parse and
> execute.


I beg to differ. While I think the second option (add another parameter to adjust the semantics of an existing parameter) would have been superior and more future-proof, we have (after long discussions) come up with a scheme where user agents can safely ignore any parameters they don't understand. This means that the meaning of xywh is cast in concrete forever. Which means that new semantics require a new parameter.

The alternative would have required a version parameter, so that old user agents would have been aware that they didn't understand the semantics of newer versions,
--
Jack Jansen, <Jack.Jansen@cwi.nl>, http://www.cwi.nl/~jack
If I can't dance I don't want to be part of your revolution -- Emma Goldman
Received on Sunday, 22 April 2012 21:43:32 UTC

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