rtp: client only needs to specify padding length and then padding indicator is set based on this

stream/rtp/encoder.go

@@ -83,7 +83,6 @@ func (e *Encoder) Write(data []byte) (int, error) {
 func (e *Encoder) Encode(payload []byte) error {
 	pkt := Pkt{
 		V:       rtpVer,           // version
-		P:       no,               // padding
 		X:       no,               // header extension
 		CC:      no,               // CSRC count
 		M:       no,               // NOTE: need to check if this works (decoders should ignore this)

stream/rtp/rtp.go

@@ -37,9 +37,10 @@ const (
 )
 
 // Pkt provides fields consistent with RFC3550 definition of an rtp packet
+// The padding indicator does not need to be set manually, only the padding length
 type Pkt struct {
 	V       byte   // Version (currently 2)
-	P       byte   // Padding indicator (0 => padding, 1 => padding)
+	p       byte   // Padding indicator (0 => padding, 1 => padding)
 	X       byte   // Extension header indicator
 	CC      byte   // CSRC count
 	M       byte   // Marker bit
@@ -57,10 +58,8 @@ func (p *Pkt) Bytes() []byte {
 		p.V = rtpVer
 	}
 
-	if p.P != 0 && p.Padding == 0 {
-		panic("Padding bit set to something other than 1, but there is no padding size defined.")
-	} else if p.P == 0 && p.Padding != 0 {
-		panic("Padding bit is set to zero, but it's indicated that there is padding.")
+	if p.Padding > 0 {
+		p.p = 1
 	}
 
 	if p.CC != 0 {
@@ -78,7 +77,7 @@ func (p *Pkt) Bytes() []byte {
 	const headSize = 3 * 4 // bytes
 	buf := make([]byte, headSize, headSize+len(p.Payload)+int(p.Padding))
 
-	buf[0] = p.V<<6 | p.P<<5 | p.CC
+	buf[0] = p.V<<6 | p.p<<5 | p.CC
 	buf[1] = p.M<<7 | p.PT
 	buf[2] = byte(p.SN >> 8)
 	buf[3] = byte(p.SN)

stream/rtp/rtp_test.go

@@ -42,7 +42,7 @@ var rtpTests = []struct {
 		num: 1,
 		pkt: Pkt{
 			V:       2,
-			P:       0,
+			p:       0,
 			X:       0,
 			CC:      0,
 			M:       0,