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Re: Range request and transcoding.

From: Martin J. Dürst <duerst@it.aoyama.ac.jp>
Date: Wed, 01 Jul 2009 18:18:34 +0900
Message-ID: <4A4B29EA.90405@it.aoyama.ac.jp>
To: Yves Lafon <ylafon@w3.org>
CC: www-tag@w3.org, public-media-fragment@w3.org
Just some random comments:

- Whether transcoding is needed or not will depend on whether the server 
has prestored a certain piece of the big picture or not. Looks like it's 
purely server-internal.

- Content-Range seems to be hard-coded to "bytes", no other unit is 
usable. (see RFC 2616, 14.16).

- For a jpeg image, because of the lossiness of the coding and the 
numeric inaccuracy of the transforms used, it may not be possible to 
reconstruct the bit-by-bit exact equivalent image from covering parts.

Regards,    Martin.

On 2009/06/30 23:26, Yves Lafon wrote:
> All,
> The Media Fragment WG is working on... defining how to identify and
> server media fragments, the primary use case is of course video, but it
> is not limited to it [1]. There is a aso a clear relation to the TAG WD
> "Usage Patterns For Client-Side URI parameters" [2], as hash parameters
> are used to generate range requests to send back to the clients only the
> desired sub-part of the resource representation.
>
> There are different axis defined, the most obvious and easy to handle is
> the time axis for video and audio, as in most cases the sub-part
> extraction can be done in the compressed domain.
>
> The geometrical axis (like asking for a clipped version of a picture or
> a video) is the origin of this email, as the WG did not reach a
> conclusion on "Is it legal to do transcoding when serving a fragment".
>
> ie: the World Map is defined by http://www.example.com/earthmap.jpg and
> is a 10000x10000 picture.
> Small country M is defined by the following URI:
> http://www.example.com/earthmap.jpg#xywh=pixel:5160,5120,32,24
>
> Suppose that we have a way to construct a ranged request out of that,
> serving only that 32x34 jpg file requires transcoding, while being
> served as a partial response.
>
> Input needed :)
> Thanks,
>
> [1] http://www.w3.org/TR/2009/WD-media-frags-reqs-20090430/
> [2] http://www.w3.org/TR/2009/WD-hash-in-uri-20090415/
>

-- 
#-# Martin J. Dürst, Professor, Aoyama Gakuin University
#-# http://www.sw.it.aoyama.ac.jp   mailto:duerst@it.aoyama.ac.jp
Received on Wednesday, 1 July 2009 09:19:44 GMT

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