title: gstreamer mux causing erroneous pipeline
body: <p>I am building a pipeline where I need to mux multiple videos(2 in this case) into a muxer(multistreamscimux). When I build the pipeline it throws errorneous pipeline: unexpected reference. </p>
  
  <p>The following png is generated out of the pipeline that muxes a single video. I am trying to create a pipe starting from rtpbin that goes into multistreamrtpscimux.rtpsrc_2. But I think I may be making a mistake in the way I specify the mux source and sink pads. I have tried the ones mentioned in <a href="https://stackoverflow.com/questions/28208964/gstreamer-pipeline-multiple-sink-to-one-src">here</a> but could not resolve it.
   Any help is appreciated.</p>
  
  <p><a href="https://i.stack.imgur.com/iFMQK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/iFMQK.png" alt="enter image description here"></a></p>
  
  <p>Here is the actual pipeline that I am trying to build.</p>
  
  <pre><code>gst-launch-1.0 -v rtpbin name=rtpbin_0  videotestsrc pattern=ball is-live=true 
  name=vidsource_0 ! video/x-raw, framerate=30/1, width=180, height=90 ! textoverlay
   text="" valignment=4 ! x264enc aud=false name=videoenc_0 ! video/x-h264,
  profile=baseline, stream-format=byte-stream,alignment=au ! rtph264pay mtu=1256 
  pt=109  ! multistreamrtpmux name=multirtpmux_0 csis-string="22446601" 
  vid-headerext-id=1 vid-header-extension-string="04" frame-marking-headerext-id=2 
  frame-marking-header-extension-string="48" ! msrtpscimux.rtpsink_0 
   multistreamrtpscimux name=msrtpscimux ! rtpbin name=rtpbin_1  videotestsrc pattern=ball
   is-live=true name=vidsource_1 ! video/x-raw, framerate=30/1, width=180, height=90
   ! textoverlay text="" valignment=4 ! x264enc aud=false name=videoenc_1 !
  video/x-h264, profile=baseline, stream-format=byte-stream,alignment=au ! 
  rtph264pay mtu=1256 pt=109  ! multistreamrtpmux name=multirtpmux_1 
  csis-string="22446601" vid-headerext-id=1 vid-header-extension-string="04" 
  frame-marking-headerext-id=2 frame-marking-header-extension-string="48" !
  multirtpmux_1.rtpsrc msrtpscimux.rtpsink_1 msrtpscimux. msrtpscimux.rtpsrc ! 
  netsim drop-probability=0.0 delay-probability=0.0 ! 
  application/x-rtp ! rtpbin_0.send_rtp_sink_0 rtpbin_0.send_rtp_src_0 !
  multisocketudpsink name=videosink rtpbin_0.send_rtcp_src_0 !  
  multisocketudpsink name=rtcpsink sync=false async=false
  </code></pre>