It was possible to generate a SDP that had an RTX payload type that matched one of the media payload types when providing caps via codec_preferences without any sink pads. Fixes m=video 9 UDP/TLS/RTP/SAVPF 96 ... a=rtpmap:96 VP8/90000 a=rtcp-fb:96 nack pli a=fmtp:96 apt=96 Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2046>