Restore VP8 munger state properly. (#1634)

* Restore VP8 munger state properly.

* clean up

pkg/sfu/codecmunger/null.go

@@ -6,6 +6,7 @@ import (
 )
 
 type Null struct {
+	seededState interface{}
 }
 
 func NewNull(_logger logger.Logger) *Null {
@@ -16,7 +17,12 @@ func (n *Null) GetState() interface{} {
 	return nil
 }
 
-func (n *Null) SeedState(_state interface{}) {
+func (n *Null) SeedState(state interface{}) {
+	n.seededState = state
+}
+
+func (n *Null) GetSeededState() interface{} {
+	return n.seededState
 }
 
 func (n *Null) SetLast(_extPkt *buffer.ExtPacket) {

pkg/sfu/codecmunger/vp8.go

@@ -64,6 +64,12 @@ func NewVP8(logger logger.Logger) *VP8 {
 	}
 }
 
+func NewVP8FromNull(cm CodecMunger, logger logger.Logger) *VP8 {
+	v := NewVP8(logger)
+	v.SeedState(cm.(*Null).GetSeededState())
+	return v
+}
+
 func (v *VP8) GetState() interface{} {
 	return VP8State{
 		ExtLastPictureId: v.extLastPictureId,

pkg/sfu/forwarder.go

@@ -256,7 +256,7 @@ func (f *Forwarder) DetermineCodec(codec webrtc.RTPCodecCapability, extensions [
 
 	switch strings.ToLower(codec.MimeType) {
 	case "video/vp8":
-		f.codecMunger = codecmunger.NewVP8(f.logger)
+		f.codecMunger = codecmunger.NewVP8FromNull(f.codecMunger, f.logger)
 		if f.vls != nil {
 			f.vls = videolayerselector.NewSimulcastFromNull(f.vls)
 		} else {