Implement empty VP8 headers.

According to RFC 7741 Section 4.4, a packetizer may ignore VP8
partition boundaries.  In that case, it might generate VP8
packets with S=0 and no data at all in the header.

codecs/codecs.go

@@ -233,7 +233,8 @@ type Flags struct {
 	Start           bool
 	End             bool
 	Keyframe        bool
-	Pid             uint16	// only returned for VP8
+	MissingPid      bool   // only returned for VP8
+	Pid             uint16 // only returned for VP8
 	Tid             uint8
 	Sid             uint8
 	TidUpSync       bool
@@ -243,7 +244,7 @@ type Flags struct {
 }
 
 func PacketFlags(codec string, buf []byte) (Flags, error) {
-	if len(buf) < 12 {
+	if len(buf) < 4 {
 		return Flags{}, errTruncated
 	}
 
@@ -267,6 +268,7 @@ func PacketFlags(codec string, buf []byte) (Flags, error) {
 		flags.Start = vp8.S != 0 && vp8.PID == 0
 		flags.End = packet.Marker
 		flags.Keyframe = vp8.S != 0 && (vp8.Payload[0]&0x1) == 0
+		flags.MissingPid = vp8.S == 0 && vp8.I == 0
 		flags.Pid = vp8.PictureID
 		flags.Tid = vp8.TID
 		flags.TidUpSync = flags.Keyframe || vp8.Y == 1
@@ -309,7 +311,7 @@ func RewritePacket(codec string, data []byte, setMarker bool, seqno uint16, delt
 		return errTruncated
 	}
 
-	if(setMarker) {
+	if setMarker {
 		data[1] |= 0x80
 	}
 
@@ -321,7 +323,7 @@ func RewritePacket(codec string, data []byte, setMarker bool, seqno uint16, delt
 
 	offset := 12
 	offset += int(data[0]&0x0F) * 4
-	if len(data) < offset+4 {
+	if len(data) <= offset {
 		return errTruncated
 	}
 
@@ -339,19 +341,30 @@ func RewritePacket(codec string, data []byte, setMarker bool, seqno uint16, delt
 		if !x {
 			return nil
 		}
-		i := (data[offset+1] & 0x80) != 0
+		offset++
+		if len(data) <= offset {
+			return errTruncated
+		}
+		i := (data[offset] & 0x80) != 0
 		if !i {
 			return nil
 		}
-		m := (data[offset+2] & 0x80) != 0
+		offset++
+		if len(data) <= offset {
+			return errTruncated
+		}
+		m := (data[offset] & 0x80) != 0
 		if m {
-			pid := (uint16(data[offset+2]&0x7F) << 8) |
+			if len(data) <= offset+1 {
-				uint16(data[offset+3])
+				return errTruncated
+			}
+			pid := (uint16(data[offset]&0x7F) << 8) |
+				uint16(data[offset+1])
 			pid = (pid + delta) & 0x7FFF
-			data[offset+2] = 0x80 | byte((pid>>8)&0x7F)
+			data[offset] = 0x80 | byte((pid>>8)&0x7F)
-			data[offset+3] = byte(pid & 0xFF)
+			data[offset+1] = byte(pid & 0xFF)
 		} else {
-			data[offset+2] = (data[offset+2] + uint8(delta)) & 0x7F
+			data[offset] = (data[offset] + uint8(delta)) & 0x7F
 		}
 		return nil
 	}

codecs/codecs_test.go

@@ -138,10 +138,19 @@ var vp8 = []byte{
 	0, 0, 0, 0,
 }
 
+var emptyVP8 = []byte{
+	0x80, 0, 0, 42,
+	0, 0, 0, 0,
+	0, 0, 0, 0,
+
+	0x00,
+}
+
 func TestPacketFlagsVP8(t *testing.T) {
 	buf := append([]byte{}, vp8...)
 	flags, err := PacketFlags("video/vp8", buf)
-	if flags.Seqno != 42 || !flags.Start || flags.Pid != 57 ||
+	if flags.Seqno != 42 || !flags.Start ||
+		flags.MissingPid || flags.Pid != 57 ||
 		flags.Sid != 0 || flags.Tid != 0 ||
 		!flags.TidUpSync || flags.Discardable || err != nil {
 		t.Errorf("Got %v, %v, %v, %v, %v, %v (%v)",
@@ -151,6 +160,19 @@ func TestPacketFlagsVP8(t *testing.T) {
 	}
 }
 
+func TestEmptyPacketFlagsVP8(t *testing.T) {
+	buf := append([]byte{}, emptyVP8...)
+	flags, err := PacketFlags("video/vp8", buf)
+	if flags.Seqno != 42 || flags.Start || !flags.MissingPid ||
+		flags.Sid != 0 || flags.Tid != 0 ||
+		flags.TidUpSync || flags.Discardable || err != nil {
+		t.Errorf("Got %v, %v, %v, %v, %v, %v (%v)",
+			flags.Seqno, flags.Start, flags.Pid, flags.Sid,
+			flags.TidUpSync, flags.Discardable, err,
+		)
+	}
+}
+
 func TestRewriteVP8(t *testing.T) {
 	for i := uint16(0); i < 0x7fff; i++ {
 		buf := append([]byte{}, vp8...)
@@ -169,6 +191,24 @@ func TestRewriteVP8(t *testing.T) {
 	}
 }
 
+func TestRewriteEmptyVP8(t *testing.T) {
+	for i := uint16(0); i < 0x7fff; i++ {
+		buf := append([]byte{}, emptyVP8...)
+		err := RewritePacket("video/vp8", buf, true, i, i)
+		if err != nil {
+			t.Errorf("rewrite: %v", err)
+			continue
+		}
+		flags, err := PacketFlags("video/vp8", buf)
+		if err != nil || flags.Seqno != i ||
+			!flags.MissingPid || !flags.Marker {
+			t.Errorf("Expected %v %v, got %v %v (%v)",
+				i, (57+i)&0x7FFF,
+				flags.Seqno, flags.Pid, err)
+		}
+	}
+}
+
 var vp9 = []byte{
 	0x80, 0, 0, 42,
 	0, 0, 0, 0,

go.mod

@@ -19,3 +19,5 @@ require (
 	golang.org/x/net v0.0.0-20220722155237-a158d28d115b // indirect
 	golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f
 )
+
+replace github.com/pion/rtp => github.com/jech/rtp v1.6.6-0.20230106211622-35cc0f7fad45

go.sum

@@ -29,6 +29,8 @@ github.com/gorilla/websocket v1.5.0/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/ad
 github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
 github.com/jech/cert v0.0.0-20210819231831-aca735647728 h1:tN+W1ll2oKuJGMCaO1CRK4rr+xSRjVSfWmnKlACdx38=
 github.com/jech/cert v0.0.0-20210819231831-aca735647728/go.mod h1:FXUA/zpiQfV4uBVN2kAwkf3X7pU7l1l2ovS45CsSYZs=
+github.com/jech/rtp v1.6.6-0.20230106211622-35cc0f7fad45 h1:VqLy+KBoTQBYgd7dqr1WwJiKmTojw+rTcAnpV97SbXk=
+github.com/jech/rtp v1.6.6-0.20230106211622-35cc0f7fad45/go.mod h1:bDb5n+BFZxXx0Ea7E5qe+klMuqiBrP+w8XSjiWtCUko=
 github.com/jech/samplebuilder v0.0.0-20220417174833-7353a593563a h1:yFkaguK4pmi0K33b8TA9T5Qoj0mZHpNPMCFdtru2yDg=
 github.com/jech/samplebuilder v0.0.0-20220417174833-7353a593563a/go.mod h1:U83y/Kl/5BrI9ceNw17+lmguIrlUlMVntxKmZmei5EA=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
@@ -71,10 +73,6 @@ github.com/pion/rtcp v1.2.8/go.mod h1:qVPhiCzAm4D/rxb6XzKeyZiQK69yJpbUDJSF7TgrqN
 github.com/pion/rtcp v1.2.9/go.mod h1:qVPhiCzAm4D/rxb6XzKeyZiQK69yJpbUDJSF7TgrqNo=
 github.com/pion/rtcp v1.2.10 h1:nkr3uj+8Sp97zyItdN60tE/S6vk4al5CPRR6Gejsdjc=
 github.com/pion/rtcp v1.2.10/go.mod h1:ztfEwXZNLGyF1oQDttz/ZKIBaeeg/oWbRYqzBM9TL1I=
-github.com/pion/rtp v1.7.0/go.mod h1:bDb5n+BFZxXx0Ea7E5qe+klMuqiBrP+w8XSjiWtCUko=
-github.com/pion/rtp v1.7.2/go.mod h1:bDb5n+BFZxXx0Ea7E5qe+klMuqiBrP+w8XSjiWtCUko=
-github.com/pion/rtp v1.7.13 h1:qcHwlmtiI50t1XivvoawdCGTP4Uiypzfrsap+bijcoA=
-github.com/pion/rtp v1.7.13/go.mod h1:bDb5n+BFZxXx0Ea7E5qe+klMuqiBrP+w8XSjiWtCUko=
 github.com/pion/sctp v1.7.10/go.mod h1:EhpTUQu1/lcK3xI+eriS6/96fWetHGCvBi9MSsnaBN0=
 github.com/pion/sctp v1.7.12/go.mod h1:xFe9cLMZ5Vj6eOzpyiKjT9SwGM4KpK/8Jbw5//jc+0s=
 github.com/pion/sctp v1.8.0/go.mod h1:xFe9cLMZ5Vj6eOzpyiKjT9SwGM4KpK/8Jbw5//jc+0s=