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Re: [SVGMobile12] Comments: Multimedia

From: Chris Lilley <chris@w3.org>
Date: Fri, 11 Nov 2005 21:22:03 +0100
Message-ID: <606207934.20051111212203@w3.org>
To: www-svg@w3.org
Cc: T Rowley <tor@cs.brown.edu>

Hello www-svg,

> 12.3.1/12.3.2
> Allowing implementations to opt-out of implementing the SVG rendering 
> model (ordering/transform) of <video> seems like a bad thing for both 
> the cleanliness of the specification and interoperability between 
> implementations.  If a graphic element is to be added to the SVG 
> specification, it should be required to be rendered according to the SVG 
> rendering model.  <video>'s "transformBehavior" and "overlay" attributes 
> should be removed along with these two sections.

We would like the world to be like that. Unfortunately the real-world
constraints of limited cpu power, battery life, etc intrude sometimes.

The way we solved this was to allow a video to be either represented as
a point or as a rectangle. In both cases, they obey the usual rules for
transformation and ordering. However, in the case of video described as
a point, the eventual on-screen location this point then becomes the
anchor for the center of the axis-aligned video.

This was necessary to allow video to be used at all on smaller devices,
and allows some useful optimisations for larger ones. It was the
cleanest way that we found while also meeting the requirements for this
much-requested feature.

> 12.4
> Unclear why it was felt necessary to add an <animation> element instead 
> of just allowing <image> to refer to SVG files.

Looking at the SMIL 2.0 specification, it became clear that SVG 1.1
should not have used an image element to point to animated vector
graphics content; SMIL differentiates between static raster and animated
vector graphics. In SVG Tiny 1.1, only raster graphics were pointed to
with the image element. SVG Tiny 1.2 continues that, and adds the
missing animation element for animated vector graphics. Also in SVG 1.2
there are further differences, regarding whether an element is timed or
not, whether it produces a viewbox or not, whether clipping is needed
(raster graphics cannot have content outside their pixel extent, while
vector graphics can have content outside their viewbox). In consequence,
we believe the division of functionality between the image and animation
elements to have been a wise one.

> 12.5
> This section describes an "audio-level" property, but samples 
> media0[124].svg use "volume".

Yes, the examples were wrong and have been corrected.

Please let us know shortly if these responses do not satisfy your

 Chris Lilley                    mailto:chris@w3.org
 Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Friday, 11 November 2005 20:22:05 UTC

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