[AVTCORE] WebRTC-HEVC Issue #27: Clarify requirement of handling symmetric/asymmetric levels of HEVC offer/answe

[Bernard Aboba <[e-mail]>]

For those of you who have dealt with H.264/AVC Offer/Answer negotiation in
WebRTC, you know that it is quite frustrating.  We would like to avoid
those problems in the WebRTC implementation of HEVC (multiple profiles,
negotiation failures due to problems in the "matching algorithm", etc.)

Here is the issue (filed by Jianlin, the developer):

"Unlike AVC, in RFC 7798 we don't explicitly signal
level-asymmetric-allowed in the SDP.

A few things that should be clarified for sendonly/sendrecv/recvonly cases
in the O/A flow for HEVC

   - level-asymmetric-allowed should be implicitly always true for HEVC.
   -
   - With a fixed profile/tier, if the offerer is able to decode/encode up
   to level 5.2, and the answerer is able to decode/encode up to level 3.1,
   what level/levels should answer include for sendonly/sendrecv/recvonly?
   -
   - With a fixed profile/tier, if the offerer is able to encode up to
   level 3.1, but decode up to level 5.2, what level/levels should offer
   include for sendonly/sendrecv/recvonly?
   -
   - With a fixed profile, if the offerer is able to encode up to level
   5.2, but decode up to level 3.1, what level/levels should the offer include
   for sendonly/sendrecv/recvonly?

There might be more combinations. So a rule should be specified for SDP
offer/answer generation."