Range request and transcoding.

[Yves Lafon]

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/

--
Baroula que barouleras, au tiéu toujou t'entourneras.

         ~~Yves

["Martin J. Dürst"]

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@...

[Julian Reschke]

Martin J. Dürst wrote:
> 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).
> ...

Fixed several months ago, see
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/85>.

BR, Julian

[Yves Lafon]

On Wed, 1 Jul 2009, "Martin J. Dürst" wrote:

> 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.
Unless the big pictures is made of tiles and served with a format using
those tiles, what's on the server side is completely opaque. In the
example I gave, I used jpeg to avoid the tiles aspect.

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

Julian already answered :)

> - 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.

Yes, that's the point. Is the bit-by-bit exact reconstruction really
mandatory/needed/desirable?
I can imagine something like
GET /earthmap.jpg HTTP/1.1
Host: www.example.com
->
HTTP/1.1 200 OK
Content-Type: image/jpeg
ETag: foo

GET /earthmap.jpg HTTP/1.1
Host: www.example.com
Range: pixel-crop xywh=5160,5120,32,24 (this is entirely made up)
->
HTTP/1.1 206 Partial Content
Content-Type: image/jpeg
ETag: W/foo
Content-Range: pixel-crop=5132,5100,64,64

Note the weak etag here to signal the possible loss of bit-by-bit
equivalence during transcoding.

> 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/
>>
>
>

--
Baroula que barouleras, au tiéu toujou t'entourneras.

         ~~Yves