main.go

package main

import (
	"context"
	"fmt"
	"io"
	"os"
	"time"

	"github.com/pion/randutil"
	"github.com/pion/webrtc/v3"
	"github.com/pion/webrtc/v3/examples/internal/signal"
	"github.com/pion/webrtc/v3/pkg/media"
	"github.com/pion/webrtc/v3/pkg/media/h264reader"
)

const (
	videoFileName = "doom.h264"
)

func main() {
	// Assert that we have an audio or video file
	_, err := os.Stat(videoFileName)
	haveVideoFile := !os.IsNotExist(err)

	// Wait for the offer to be pasted
	offer := webrtc.SessionDescription{}
	signal.Decode(signal.MustReadStdin(), &offer)

	// We make our own mediaEngine so we can place the sender's codecs in it.  This because we must use the
	// dynamic media type from the sender in our answer. This is not required if we are the offerer
	mediaEngine := webrtc.MediaEngine{}
	if err = mediaEngine.PopulateFromSDP(offer); err != nil {
		panic(err)
	}

	// Create a new RTCPeerConnection
	api := webrtc.NewAPI(webrtc.WithMediaEngine(mediaEngine))
	peerConnection, err := api.NewPeerConnection(webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	})
	if err != nil {
		panic(err)
	}
	iceConnectedCtx, iceConnectedCtxCancel := context.WithCancel(context.Background())

	if haveVideoFile {
		// Create a video track
		videoTrack, addTrackErr := peerConnection.NewTrack(getPayloadType(mediaEngine, webrtc.RTPCodecTypeVideo, "H264"), randutil.NewMathRandomGenerator().Uint32(), "video", "pion")
		if addTrackErr != nil {
			panic(addTrackErr)
		}
		if _, addTrackErr = peerConnection.AddTrack(videoTrack); addTrackErr != nil {
			panic(addTrackErr)
		}

		go func() {
			file, h264Err := os.Open(videoFileName)
			if h264Err != nil {
				panic(h264Err)
			}

			h264, h264Err := h264reader.NewWith(file)
			if h264Err != nil {
				panic(h264Err)
			}

			// Wait for connection established
			<-iceConnectedCtx.Done()

			spsAndPpsCache := []byte{}
			for {
				nal, h264Err := h264.NextNAL()
				if h264Err == io.EOF {
					fmt.Printf("All video frames parsed and sent")
					os.Exit(0)
				}
				if h264Err != nil {
					panic(h264Err)
				}

				time.Sleep(time.Millisecond * 33)

				nal.Data = append([]byte{0x00, 0x00, 0x00, 0x01}, nal.Data...)

				if nal.UnitType == h264reader.NalUnitTypeSPS || nal.UnitType == h264reader.NalUnitTypePPS {
					spsAndPpsCache = append(spsAndPpsCache, nal.Data...)
					continue
				} else if nal.UnitType == h264reader.NalUnitTypeCodedSliceIdr {
					nal.Data = append(spsAndPpsCache, nal.Data...)
					spsAndPpsCache = []byte{}
				}

				if h264Err = videoTrack.WriteSample(media.Sample{Data: nal.Data, Samples: 90000}); h264Err != nil {
					panic(h264Err)
				}
			}
		}()
	}

	// Set the handler for ICE connection state
	// This will notify you when the peer has connected/disconnected
	peerConnection.OnICEConnectionStateChange(func(connectionState webrtc.ICEConnectionState) {
		fmt.Printf("Connection State has changed %s \n", connectionState.String())
		if connectionState == webrtc.ICEConnectionStateConnected {
			iceConnectedCtxCancel()
		}
	})

	// Set the remote SessionDescription
	if err = peerConnection.SetRemoteDescription(offer); err != nil {
		panic(err)
	}

	// Create answer
	answer, err := peerConnection.CreateAnswer(nil)
	if err != nil {
		panic(err)
	}

	// Create channel that is blocked until ICE Gathering is complete
	gatherComplete := webrtc.GatheringCompletePromise(peerConnection)

	// Sets the LocalDescription, and starts our UDP listeners
	if err = peerConnection.SetLocalDescription(answer); err != nil {
		panic(err)
	}

	// Block until ICE Gathering is complete, disabling trickle ICE
	// we do this because we only can exchange one signaling message
	// in a production application you should exchange ICE Candidates via OnICECandidate
	<-gatherComplete

	// Output the answer in base64 so we can paste it in browser
	fmt.Println(signal.Encode(*peerConnection.LocalDescription()))

	// Block forever
	select {}
}

// Search for Codec PayloadType
//
// Since we are answering we need to match the remote PayloadType
func getPayloadType(m webrtc.MediaEngine, codecType webrtc.RTPCodecType, codecName string) uint8 {
	for _, codec := range m.GetCodecsByKind(codecType) {
		if codec.Name == codecName {
			return codec.PayloadType
		}
	}
	panic(fmt.Sprintf("Remote peer does not support %s", codecName))
}