Subject: [clue] Capture Attribute Discussion: 4.5. Priority

From: Christian Groves <[email-masked]>
Date: Thu, 13 Dec 2012 14:37:08 +1100

Hello

The priority attribute is described in draft-groves-clue-capture-attr:

"4.5.   Priority

    As has been highlighted in discussions on the CLUE mailing list there
    appears to be some desire to provide some relative priority between
    captures when multiple alternatives are supplied.  This priority can
    be used to determine which captures contain the most important
    information (according to the provider).  This may be important in
    case where the consumer has limited resources and can on render a
    subset of captures.  Priority may also be advantageous in congestion
    scenarios where media from one capture may be favoured over other
    captures in any control algorithms.  This could be supplied via
    "ordering" in a CLUE data structure however this may be problematic
    if people assume some spatial meaning behind ordering, i.e. given
    three captures VC1, VC2, VC3: it would be natural to send VC1,VC2,VC3
    if the images are composed this way.  However if your boss sits in
    the middle view the priority may be VC2,VC1,VC3.  Explicit signalling
    is better.

    Additionally currently there are no hints to relative priority among
    captures from different capture scenes.  In order to prevent any
    misunderstanding with implicit ordering a numeric number that may be
    assigned to each capture.

    The "priority" attribute indicates a relative priority between
    captures.  For example it is possible to assign a priority between
    two presentation captures that would allow a remote endpoint to
    determine which presentation is more important.  Priority is assigned
    at the individual capture level.  It represents the provider's view
    of the relative priority between captures with a priority.  The same
    priority number may be used across multiple captures.  It indicates
    they are equally as important.  If no priority is assigned no
    assumptions regarding relative important of the capture can be
    assumed."

In recent discussions about clarifications for scenes I think it was 
agreed? that the framework syntax doesn't imply any relative priority. 
So if a priority mechanism is needed then an attribute would be 
required. Priority may be needed if the metadata (other attributes) 
isn't sufficient to describe a capture. This attribute isn't motivated 
by support for any preference or emergency scheme. Do people have 
concerns about adding this to the framework?

Regards, Christian