[avtext] Frame marking & VP9 SVC

[Sergio Garcia Murillo <[e-mail]>]

Hi,

I have been implementing the framemarking for PERC and I have some 
doubts regarding the VP9 LID mapping.

First, is that according to 
https://tools.ietf.org/html/draft-ietf-payload-vp9-03 there are no 
quality layers on VP9 SVC they are considered as case of spatial layers:

    VP9 supports quality layers as spatial layers without any resolution
    changes; hereinafter, the term "spatial layer" is used to represent
    both spatial and quality layers.

So, shouldn't the LID reference to the spatial layer ID only  and omit 
the quality layer id completely? Also, the spatial layer id is 3 bits on 
that draft.

Also, in order to be able to implement VP9 SVC layer selection, the SFU 
needs the information of the P and U bits of the VP9 header description:

    P: Inter-picture predicted layer frame.  When set to zero, the layer
       frame does not utilize inter-picture prediction.  In this case,
       up-switching to current spatial layer's frame is possible from
       directly lower spatial layer frame.  P SHOULD also be set to zero
       when encoding a layer synchronization frame in response to an LRR
       [I-D.ietf-avtext-lrr 
<https://tools.ietf.org/html/draft-ietf-payload-vp9-03#ref-I-D.ietf-avtext-lrr>] message (seeSection 5.4 
<https://tools.ietf.org/html/draft-ietf-payload-vp9-03#section-5.4>).  When P is set to
       zero, the T bit (described below) MUST also be set to 0 (if
       present).

    U: Switching up point.  If this bit is set to 1 for the current
       frame with temporal layer ID equal to T, then "switch up" to a
       higher frame rate is possible as subsequent higher temporal
       layer frames will not depend on any frame before the current
       frame (in coding time) with temporal layer ID greater than T.


Without that info, the SFU won't be able to upscale, so it would be 
required to add that information on the VP9 LID.
Including that changes, it would be something like this:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  ID=2 |  L=2  |S|E|I|D|B| TID |0|0|0|P|U|SID  |    TL0PICIDX  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Best regards
Sergio