Two different documentation entries for RtpSession
Under https://gstreamer.freedesktop.org/documentation/rtpmanager/?gi-language=c
you have rtpsession and RtpSession. RtpSession seems more up to date, it has more properties.
Under https://gstreamer.freedesktop.org/documentation/rtpmanager/?gi-language=c
you have rtpsession and RtpSession. RtpSession seems more up to date, it has more properties.