I’ve solved the issue, it just needs an sdp file like this:
v=0
m=video 5000 RTP/AVP 96
c=IN IP4 127.0.0.1
a=rtpmap:96 MP4V-ES/90000
and the option “send-config=true” for the rtpmp4vpay element:
gst-launch videotestsrc ! ffenc_mpeg4 ! rtpmp4vpay send-config=true ! udpsink host=127.0.0.1 port=5000
and then, it can be played with
vlc <filename>.sdp