Enable TWCC by default

Add functions to configure TWCC reports and TWCC header extensions.
Only TWCC reports are enabled by default, because there is no Congestion
Controller available to handle reports from a remote peer, yet.

interceptor.go

@@ -8,7 +8,9 @@ import (
 	"github.com/pion/interceptor"
 	"github.com/pion/interceptor/pkg/nack"
 	"github.com/pion/interceptor/pkg/report"
+	"github.com/pion/interceptor/pkg/twcc"
 	"github.com/pion/rtp"
+	"github.com/pion/sdp/v3"
 )
 
 // RegisterDefaultInterceptors will register some useful interceptors.
@@ -23,6 +25,10 @@ func RegisterDefaultInterceptors(mediaEngine *MediaEngine, interceptorRegistry *
 		return err
 	}
 
+	if err := ConfigureTWCCSender(mediaEngine, interceptorRegistry); err != nil {
+		return err
+	}
+
 	return nil
 }
 
@@ -62,6 +68,36 @@ func ConfigureNack(mediaEngine *MediaEngine, interceptorRegistry *interceptor.Re
 	return nil
 }
 
+// ConfigureTWCCHeaderExtensionSender will setup everything necessary for adding
+// a TWCC header extension to outgoing RTP packets. This will allow the remote peer to generate TWCC reports.
+func ConfigureTWCCHeaderExtensionSender(mediaEngine *MediaEngine, interceptorRegistry *interceptor.Registry) error {
+	err := mediaEngine.RegisterHeaderExtension(RTPHeaderExtensionCapability{URI: sdp.TransportCCURI}, RTPCodecTypeVideo)
+	if err != nil {
+		return err
+	}
+	i, err := twcc.NewHeaderExtensionInterceptor()
+	if err != nil {
+		return err
+	}
+	interceptorRegistry.Add(i)
+	return err
+}
+
+// ConfigureTWCCSender will setup everything necessary for generating TWCC reports.
+func ConfigureTWCCSender(mediaEngine *MediaEngine, interceptorRegistry *interceptor.Registry) error {
+	mediaEngine.RegisterFeedback(RTCPFeedback{Type: TypeRTCPFBTransportCC}, RTPCodecTypeVideo)
+	err := mediaEngine.RegisterHeaderExtension(RTPHeaderExtensionCapability{URI: sdp.TransportCCURI}, RTPCodecTypeVideo)
+	if err != nil {
+		return err
+	}
+	generator, err := twcc.NewSenderInterceptor()
+	if err != nil {
+		return err
+	}
+	interceptorRegistry.Add(generator)
+	return nil
+}
+
 type interceptorToTrackLocalWriter struct{ interceptor atomic.Value } // interceptor.RTPWriter }
 
 func (i *interceptorToTrackLocalWriter) WriteRTP(header *rtp.Header, payload []byte) (int, error) {