Use abs-send-time RTP header extension for video downstream (#149)

- Update ion-sfu to v1.20.14
- Enable `abs-send-time` for video tracks

Reference: ion-sfu PR - https://github.com/livekit/ion-sfu/pull/12

Testing:
--------
- Look at SDP offer in subscriber PC and ensure that abs-send-time is negotiated.
- Ensure that downstream packets have `abs-send-time` extension for video packets.

TODO:
-----
- Not yet setting this for audio tracks. Eventually we want to move
to TWCC. This is just a step along the way.

pkg/rtc/mediaengine.go

@@ -87,6 +87,15 @@ func createPubMediaEngine(codecs []*livekit.Codec) (*webrtc.MediaEngine, error)
 
 func createSubMediaEngine() (*webrtc.MediaEngine, error) {
 	me := &webrtc.MediaEngine{}
+
+	for _, extension := range []string{
+		sdp.ABSSendTimeURI,
+	} {
+		if err := me.RegisterHeaderExtension(webrtc.RTPHeaderExtensionCapability{URI: extension}, webrtc.RTPCodecTypeVideo); err != nil {
+			return nil, err
+		}
+	}
+
 	return me, nil
 }
 

pkg/rtc/mediatrack.go

@@ -205,6 +205,9 @@ func (t *MediaTrack) AddSubscriber(sub types.Participant) error {
 		}
 	}
 
+	sendParameters := sender.GetParameters()
+	downTrack.SetRTPHeaderExtensions(sendParameters.HeaderExtensions)
+
 	downTrack.SetTransceiver(transceiver)
 	// when outtrack is bound, start loop to send reports
 	downTrack.OnBind(func() {

pkg/service/wire_gen.go

@@ -1,7 +1,8 @@
 // Code generated by Wire. DO NOT EDIT.
 
 //go:generate go run github.com/google/wire/cmd/wire
-//+build !wireinject
+//go:build !wireinject
+// +build !wireinject
 
 package service