Add vp9 svc support by Dependency Descriptor (#1586)

* Add VP9 SVC support

* Fix preferred fps does not work

* Fix forwarder test

pkg/sfu/buffer/buffer.go

@@ -564,6 +564,8 @@ func (b *Buffer) getExtPacket(rtpPacket *rtp.Packet, arrivalTime int64) *ExtPack
 		ep.KeyFrame = IsH264Keyframe(rtpPacket.Payload)
 	case "video/av1":
 		ep.KeyFrame = IsAV1Keyframe(rtpPacket.Payload)
+	case "video/vp9":
+		ep.KeyFrame = IsVP9Keyframe(rtpPacket.Payload)
 	}
 
 	if ep.KeyFrame {

pkg/sfu/buffer/helpers.go

@@ -4,6 +4,8 @@ import (
 	"encoding/binary"
 	"errors"
 
+	"github.com/pion/rtp/codecs"
+
 	"github.com/livekit/protocol/logger"
 )
 
@@ -351,4 +353,28 @@ func IsAV1Keyframe(payload []byte) bool {
 	}
 }
 
+// IsVP9Keyframe detects if vp9 payload is a keyframe
+// taken from https://github.com/jech/galene/blob/master/codecs/codecs.go
+// all credits belongs to Juliusz Chroboczek @jech and the awesome Galene SFU
+func IsVP9Keyframe(payload []byte) bool {
+	var vp9 codecs.VP9Packet
+	_, err := vp9.Unmarshal(payload)
+	if err != nil || len(vp9.Payload) < 1 {
+		return false
+	}
+	if !vp9.B {
+		return false
+	}
+
+	if (vp9.Payload[0] & 0xc0) != 0x80 {
+		return false
+	}
+
+	profile := (vp9.Payload[0] >> 4) & 0x3
+	if profile != 3 {
+		return (vp9.Payload[0] & 0xC) == 0
+	}
+	return (vp9.Payload[0] & 0x6) == 0
+}
+
 // -------------------------------------