Forwarding downstream PLIs from readers back up to publishers

[tmatth]

Question

I'm using mediamtx as a proxy to another RTSP server. Readers reading from mediamtx will send a PLI when needed, but I'd like to forward that PLI to the upstream source/publisher. I believe mediamtx simply swallows the incoming RTCP traffic it gets from players. I've added some logging here:

+diff --git a/internal/servers/rtsp/session.go b/internal/servers/rtsp/session.go
+index a3e7a90..eab1bb9 100644
+--- a/internal/servers/rtsp/session.go
++++ b/internal/servers/rtsp/session.go
+@@ -11,8 +11,10 @@ import (
+       "github.com/bluenviron/gortsplib/v4"
+       rtspauth "github.com/bluenviron/gortsplib/v4/pkg/auth"
+       "github.com/bluenviron/gortsplib/v4/pkg/base"
++      "github.com/bluenviron/gortsplib/v4/pkg/description"
+       "github.com/google/uuid"
+       "github.com/pion/rtp"
++      "github.com/pion/rtcp"
+ 
+       "github.com/bluenviron/mediamtx/internal/auth"
+       "github.com/bluenviron/mediamtx/internal/conf"
+@@ -259,6 +261,19 @@ func (s *session) onPlay(_ *gortsplib.ServerHandlerOnPlayCtx) (*base.Response, e
+                       Query:           s.rsession.SetuppedQuery(),
+               })
+ 
++              for _, medi := range s.rsession.SetuppedMedias() {
++                      for _, _ = range medi.Formats {
++                              s.rsession.OnPacketRTCPAny(func(medi *description.Media, pkt rtcp.Packet) {
++                                      switch p := pkt.(type) {
++                                      case *rtcp.PictureLossIndication:
++                                              s.Log(logger.Warn, "GOT PLI packet %v, %v", pkt, p)
++                                              // TODO: forward this PLI to original publisher
++                                      default:
++                                              s.Log(logger.Warn, "GOT RTCP packet %v, %v", pkt, p)
++                                      }
++                              })
++                      }
++              }
++
+               s.mutex.Lock()
+               s.state = gortsplib.ServerSessionStatePlay
+               s.transport = s.rsession.SetuppedTransport()

How can I access the underlying publisher and forward the RTCP PLI packet to it?

[neilyoung]

That would interest me too...