This is for the rtpengine module.
The rtpengine daemon supports lists and dictionaries over the 'ng' protocol. These are required to access some features. From the doc page:
Lists and dictionaries are supported in this format using square brackets [ ], for example:
{ "rtpp_flags": "via-branch=auto-next OSRTP=[accept] codec=[transcode=[PCMA PCMU] accept=[AMR-WB AMR] strip=[EVS]]" }
One such command is sdp-media-remove, which requires a list. In Kamailio invokes it like this to remove the video, message and image streams from the SDP:
rtpengine_offer("sdp-media-remove=[video message image]")
Can we adopt the same syntax in OpenSIPS as well?