Finish RTCRtpReceiver and RTCRtpSender

Allow sending of media via ORTC, examples will be added in the future.
But for now all of this state has been pulled out of RTCPeerConnection

Resolves #312

rtctrack.go

@@ -1,22 +1,71 @@
 package webrtc
 
 import (
+	"crypto/rand"
+	"encoding/binary"
+
 	"github.com/pions/webrtc/pkg/media"
 	"github.com/pions/webrtc/pkg/rtcp"
 	"github.com/pions/webrtc/pkg/rtp"
+	"github.com/pkg/errors"
 )
 
 // RTCTrack represents a track that is communicated
 type RTCTrack struct {
+	isRawRTP bool
+
 	ID          string
 	PayloadType uint8
 	Kind        RTCRtpCodecType
 	Label       string
 	Ssrc        uint32
 	Codec       *RTCRtpCodec
+
 	Packets     <-chan *rtp.Packet
 	RTCPPackets <-chan rtcp.Packet
-	Samples     chan<- media.RTCSample
-	RawRTP      chan<- *rtp.Packet
-	isRawRTP    bool
+
+	Samples chan<- media.RTCSample
+	RawRTP  chan<- *rtp.Packet
+}
+
+// NewRawRTPTrack initializes a new *RTCTrack configured to accept raw *rtp.Packet
+//
+// NB: If the source RTP stream is being broadcast to multiple tracks, each track
+// must receive its own copies of the source packets in order to avoid packet corruption.
+func NewRawRTPTrack(payloadType uint8, ssrc uint32, id, label string) (*RTCTrack, error) {
+	if ssrc == 0 {
+		return nil, errors.New("SSRC supplied to NewRawRTPTrack() must be non-zero")
+	}
+
+	return &RTCTrack{
+		isRawRTP: true,
+
+		ID:          id,
+		PayloadType: payloadType,
+		Label:       label,
+		Ssrc:        ssrc,
+	}, nil
+}
+
+// NewRTCSampleTrack initializes a new *RTCTrack configured to accept media.RTCSample
+func NewRTCSampleTrack(payloadType uint8, id, label string, codec *RTCRtpCodec) (*RTCTrack, error) {
+	if codec == nil {
+		return nil, errors.New("codec supplied to NewRTCSampleTrack() must not be nil")
+	}
+
+	buf := make([]byte, 4)
+	if _, err := rand.Read(buf); err != nil {
+		return nil, errors.New("failed to generate random value")
+	}
+
+	return &RTCTrack{
+		isRawRTP: false,
+
+		ID:          id,
+		PayloadType: payloadType,
+		Kind:        codec.Type,
+		Label:       label,
+		Ssrc:        binary.LittleEndian.Uint32(buf),
+		Codec:       codec,
+	}, nil
 }