Some questions about RTCRtpEncodingParameters...

Another set of questions I had about the Editor's draft relates to RTCRtpEncodingParameters, which is defined as follows:

dictionary RTCRtpEncodingParameters {
    unsigned int?        ssrc = null;
    DOMString?           codecName = "";
    RTCRtpFecParameters? fec;
    RTCRtpRtxParameters? rtx;
    double               priority = 1.0;
    double               maxBitrate = null;
    double               minQuality = null;
    double               frameratebias = 0.5;
    double               scale = null;
    boolean              active = true;
    DOMString?           encodingId;
    sequence<DOMString>  dependencyEncodingIds;
};

To take this for a spin, I looked at how it might be used to handle a few use cases:


a.       Temporal scalability;

b.      Spatial simulcast combined with temporal scalability.

Maybe it's just me, but it seemed that there was some missing functionality.

For example, while the encodingId and dependencyEncodingIds can be used to set up layering, to do layering and simulcast together requires setting up multiple sender objects.   This leaves the application having to deal with tradeoffs between simulcast and layering, which could be challenging.  Also, the above RTCRtpEncodingParameters object doesn't seem to be able to handle temporal scalabiltiy, only spatial (via the scale attribute).  This is because there is no "framescale" attribute to provide instruction on how to divide the framerate between the various layers.

Also, it occurred to me that a developer attempting to set up the RTCRtpEncodiingParameters object correctly might encounter quite a few challenges.    This object seems like it would be best set up automatically under the covers based on some general developer-provided preferences -- something very high level like "I want SVC if it is available, figure out what will work best".   The browser should be able to figure this out based on the "capabilities" of each peer, such as the number of layers that the encoder/decoder can handle of each layering type  (e.g. temporal, spatial, quality), or information about simulcast capabilities (e.g. the maximum number of simulcast streams that the encoder can handle).

Some other questions relating to whether these attributes make sense for SVC at all.
For example, priority makes sense for specifying the priority between audio and video - but what does it mean when it is specified in individual SVC layers?

Similarly, minQuality might make some sense for a base layer (as might minFrameRate or minResolution), but what does it mean to specify this at each SVC layer?

Also, is it necessary to provide a maxBitrate knob for each layer in SVC?