Enhance support of NMOS stream mappings for JPEG XS and e.g. H264, H265, VP9 and AV1

[garethsb]

NMOS supports compressed video streams; at the most basic via the media_type attribute in the Flow and the media_types capability in the Receiver.

Since IS-04 v1.3, we can register new Flow attributes, and with BCP-004-01 Receiver Capabilities and the Capabilities register, new Receiver capabilities. For example, for JPEG XS (see #177), it was agreed that bit rate is an important characteristic to add (as well as being able to indicate color (sub-)sampling for coded video Flows via the same components attribute used for raw video Flows).

The nmos-cpp sdp module is generic and extensible.

However, the nmos-cpp _nmos/sdp_utils.h_ module and the nmos::sdp_parameters structure it defines are not.

I propose we extend the nmos::sdp_parameters and related functions to provide SDP read/write for additional media types. If it cannot be done maintaining backward compatibility we can do something alongside instead.

There may be no point making something fully generic if it wouldn't provide any abstraction over the lower level sdp namespace functions.

Top priorities are to support video/jxsv, video/H264, video/H265, video/VP9, video/AV1 and audio/AM824 (which doesn't appear to have an IANA registration...).

I feel the nmos::sdp_parameters structure should expose all the required and optional format-specific parameters of these media types as first-class values. There are currently a few missing even for video/raw (when used as per ST 2110-20) such as CMAX (noted in the code).

[garethsb]

Missing format-specific parameters etc.:

• video/raw (when used as per ST 2110-20/-21)
  • Required parameters
  • PM, SSN (currently written with hard-coded values and not read)
  • Optional parameters
  • RANGE
  • MAXUDP
  • PAR
  • TROFF (also for video/SMPTE2022-6 when used as per ST 2022-8)
  • CMAX
• video/SMPTE2022-6
  • Other
  • Frame rate as a=framerate:
• video/jxsv
  • Required parameters
  • packetmode
  • Optional parameters
  • transmode
  • profile
  • level
  • sublevel
  • ~depth~ (same as video/raw per ST 2110-20)
  • ~width~
  • ~height~
  • ~exactframerate~
  • ~interlace~
  • ~segmented~
  • ~sampling~
  • ~colorimetry~
  • ~TCS~
  • RANGE (as per video/raw, ST 2110-20)
  • Other
  • Bit rate in a b=AS: application-specific bandwidth information line
• video/H264
  • Optional parameters (see https://datatracker.ietf.org/doc/html/rfc6184#section-8.2.3)
  • profile-level-id
  • sprop-parameter-sets
  • sprop-level-parameter-sets
  • packetization-mode
  • sprop-interleaving-depth
  • sprop-deint-buf-req
  • sprop-init-buf-time
  • sprop-max-don-diff
  • Note: there are also a large number of H264 receiver capabilities defined which could be mapped to BCP-004-01 Receiver Capabilities?
• video/H265
  • Optional parameters
  • profile-space
  • profile-id
  • tier-flag
  • level-id
  • profile-compatibility-indicator
  • sprop-sub-layer-id
  • tx-mode
  • sprop-vps
  • sprop-sps
  • sprop-pps
  • sprop-sei
  • sprop-max-don-diff
  • sprop-depack-buf-nalus
  • sprop-depack-buf-bytes
  • sprop-segmentation-id
  • sprop-spatial-segmentation-idc
  • Note: there are also a large number of H265 receiver capabilities defined which could be mapped to BCP-004-01 Receiver Capabilities?
• video/VP9
  • Optional parameters
  • profile-id
• video/AV1
  • Optional parameters
  • profile
  • level-idx
  • tier
• audio/L
  • Other
  • Maximum packet time in an a=maxptime: attribute
• audio/AM824 (per ST 2110-31, since there's no IANA registration...)
  • ~channel-order~ (same as ST 2110-30)

[garethsb]

Other media types mentioned in #200: video/vc2, and audio/aac, /mp2, /mp3, /m4a, /opus. Relative priority unknown!

[garethsb]

Of the missing format-specific parameters etc. mentioned in https://github.com/sony/nmos-cpp/issues/213#issuecomment-979016210, for the currently supported media types (video/raw, video/jxsv, video/SMPTE2022-6, audio/L), I think they've all been implemented in #280 apart from a=framerate: roundtrip through video_SMPTE2022_6_parameters...

Therefore, let's close this issue and wait for BCP-006-xx for video/H264, etc.