Count padding bytes in telemetry (#264)

Count padding bytes in telemetry outgoing total bytes

pkg/rtc/mediatrack.go

@@ -267,6 +267,9 @@ func (t *MediaTrack) AddSubscriber(sub types.Participant) error {
 	downTrack.OnPacketSent(func(_ *sfu.DownTrack, size int) {
 		t.params.Telemetry.OnDownstreamPacket(sub.ID(), size)
 	})
+	downTrack.OnPaddingSent(func(_ *sfu.DownTrack, size int) {
+		t.params.Telemetry.OnDownstreamPacket(sub.ID(), size)
+	})
 	downTrack.OnRTCP(func(pkts []rtcp.Packet) {
 		t.params.Telemetry.HandleRTCP(livekit.StreamType_DOWNSTREAM, sub.ID(), pkts)
 	})

pkg/sfu/downtrack.go

@@ -120,6 +120,9 @@ type DownTrack struct {
 
 	// packet sent callback
 	onPacketSent []func(dt *DownTrack, size int)
+
+	// padding packet sent callback
+	onPaddingSent []func(dt *DownTrack, size int)
 }
 
 // NewDownTrack returns a DownTrack.
@@ -375,12 +378,9 @@ func (d *DownTrack) WritePaddingRTP(bytesToSend int) int {
 
 		size := hdr.MarshalSize() + len(payload)
 		d.UpdatePaddingStats(uint32(size))
-		// LK-TOOD-START:
-		// Maybe call onPacketSent callbacks? But, a couple of issues to think about
-		//   - Analytics - should padding bytes be counted?
-		//   - StreamAllocator probing - should not include padding
-		// Maybe a separate callback for `onPaddingSent`?
-		// LK-TODO-END
+		for _, f := range d.onPaddingSent {
+			f(d, size)
+		}
 
 		// LK-TODO-START
 		// NACK buffer for these probe packets.
@@ -510,6 +510,10 @@ func (d *DownTrack) OnPacketSent(fn func(dt *DownTrack, size int)) {
 	d.onPacketSent = append(d.onPacketSent, fn)
 }
 
+func (d *DownTrack) OnPaddingSent(fn func(dt *DownTrack, size int)) {
+	d.onPaddingSent = append(d.onPaddingSent, fn)
+}
+
 func (d *DownTrack) IsDeficient() bool {
 	return d.forwarder.IsDeficient()
 }