fix bug that prevented multiple readers from accessing the same stream (#2281) (#2282)

internal/core/webrtc_outgoing_track.go

@@ -363,7 +363,5 @@ func (t *webRTCOutgoingTrack) start(
 		}
 	}()
 
-	stream.AddReader(writer, t.media, t.format, func(u unit.Unit) error {
-		return t.cb(u)
-	})
+	stream.AddReader(writer, t.media, t.format, t.cb)
 }

internal/stream/stream_format.go

@@ -80,8 +80,9 @@ func (sf *streamFormat) writeUnit(s *Stream, medi *description.Media, u unit.Uni
 	}
 
 	for writer, cb := range sf.readers {
+		ccb := cb
 		writer.Push(func() error {
-			return cb(u)
+			return ccb(u)
 		})
 	}
 }