Fix handling of empty RTP payloads with padding (#163)

service/rtc/sfu.go

@@ -488,6 +488,15 @@ func (s *Server) InitSession(cfg SessionConfig, closeCb func() error) error {
 					return
 				}
 
+				// Mitigating against https://github.com/pion/webrtc/issues/2403
+				// The padding will be stripped by pion but the header bit will be forwarded as is (set).
+				// This causes clients (e.g. calls-transcriber) to fail to decode the packet.
+				// Since the payload is empty, we simply reset the padding to 0.
+				if packet.Padding && len(packet.Payload) == 0 {
+					packet.Padding = false
+					packet.PaddingSize = 0
+				}
+
 				if hasVAD {
 					var ext rtp.AudioLevelExtension
 					audioExtData := packet.GetExtension(uint8(audioLevelExtensionID))
@@ -644,6 +653,15 @@ func (s *Server) InitSession(cfg SessionConfig, closeCb func() error) error {
 					return
 				}
 
+				// Mitigating against https://github.com/pion/webrtc/issues/2403
+				// The padding will be stripped by pion but the header bit will be forwarded as is (set).
+				// This causes clients (e.g. calls-transcriber) to fail to decode the packet.
+				// Since the payload is empty, we simply reset the padding to 0.
+				if packet.Padding && len(packet.Payload) == 0 {
+					packet.Padding = false
+					packet.PaddingSize = 0
+				}
+
 				rm.PushSample(packet.MarshalSize())
 				if limiter.Allow() {
 					rate, dur := rm.GetRate()