main.go

// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT

//go:build !js
// +build !js

// gstreamer-receive is a simple application that shows how to receive media using Pion WebRTC and play live using GStreamer.
package main

import (
	"bufio"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"strings"
	"time"

	"github.com/go-gst/go-gst/gst"
	"github.com/go-gst/go-gst/gst/app"
	"github.com/pion/rtcp"
	"github.com/pion/webrtc/v4"
)

func main() {
	// Initialize GStreamer
	gst.Init(nil)

	// Everything below is the Pion WebRTC API! Thanks for using it ❤️.

	// Prepare the configuration
	config := webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	}

	// Create a new RTCPeerConnection
	peerConnection, err := webrtc.NewPeerConnection(config)
	if err != nil {
		panic(err)
	}

	// Set a handler for when a new remote track starts, this handler creates a gstreamer pipeline
	// for the given codec
	peerConnection.OnTrack(func(track *webrtc.TrackRemote, _ *webrtc.RTPReceiver) {
		if track.Kind() == webrtc.RTPCodecTypeVideo {
			// Send a PLI on an interval so that the publisher is pushing a keyframe every rtcpPLIInterval
			go func() {
				ticker := time.NewTicker(time.Second * 3)
				for range ticker.C {
					rtcpSendErr := peerConnection.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: uint32(track.SSRC())}})
					if rtcpSendErr != nil {
						fmt.Println(rtcpSendErr)
					}
				}
			}()
		}

		codecName := strings.Split(track.Codec().RTPCodecCapability.MimeType, "/")[1]
		fmt.Printf("Track has started, of type %d: %s \n", track.PayloadType(), codecName)

		appSrc := pipelineForCodec(track, codecName)
		buf := make([]byte, 1400)
		for {
			i, _, readErr := track.Read(buf)
			if readErr != nil {
				panic(err)
			}

			appSrc.PushBuffer(gst.NewBufferFromBytes(buf[:i]))
		}
	})

	// 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())
	})

	// Wait for the offer to be pasted
	offer := webrtc.SessionDescription{}
	decode(readUntilNewline(), &offer)

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

	// Create an 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
	err = peerConnection.SetLocalDescription(answer)
	if 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(encode(peerConnection.LocalDescription()))

	// Block forever
	select {}
}

// Create the appropriate GStreamer pipeline depending on what codec we are working with
func pipelineForCodec(track *webrtc.TrackRemote, codecName string) *app.Source {
	pipelineString := "appsrc format=time is-live=true do-timestamp=true name=src ! application/x-rtp"
	switch strings.ToLower(codecName) {
	case "vp8":
		pipelineString += fmt.Sprintf(", payload=%d, encoding-name=VP8-DRAFT-IETF-01 ! rtpvp8depay ! decodebin ! autovideosink", track.PayloadType())
	case "opus":
		pipelineString += fmt.Sprintf(", payload=%d, encoding-name=OPUS ! rtpopusdepay ! decodebin ! autoaudiosink", track.PayloadType())
	case "vp9":
		pipelineString += " ! rtpvp9depay ! decodebin ! autovideosink"
	case "h264":
		pipelineString += " ! rtph264depay ! decodebin ! autovideosink"
	case "g722":
		pipelineString += " clock-rate=8000 ! rtpg722depay ! decodebin ! autoaudiosink"
	default:
		panic("Unhandled codec " + codecName) //nolint
	}

	pipeline, err := gst.NewPipelineFromString(pipelineString)
	if err != nil {
		panic(err)
	}

	if err = pipeline.SetState(gst.StatePlaying); err != nil {
		panic(err)
	}

	appSrc, err := pipeline.GetElementByName("src")
	if err != nil {
		panic(err)
	}

	return app.SrcFromElement(appSrc)
}

// Read from stdin until we get a newline
func readUntilNewline() (in string) {
	var err error

	r := bufio.NewReader(os.Stdin)
	for {
		in, err = r.ReadString('\n')
		if err != nil && !errors.Is(err, io.EOF) {
			panic(err)
		}

		if in = strings.TrimSpace(in); len(in) > 0 {
			break
		}
	}

	fmt.Println("")
	return
}

// JSON encode + base64 a SessionDescription
func encode(obj *webrtc.SessionDescription) string {
	b, err := json.Marshal(obj)
	if err != nil {
		panic(err)
	}

	return base64.StdEncoding.EncodeToString(b)
}

// Decode a base64 and unmarshal JSON into a SessionDescription
func decode(in string, obj *webrtc.SessionDescription) {
	b, err := base64.StdEncoding.DecodeString(in)
	if err != nil {
		panic(err)
	}

	if err = json.Unmarshal(b, obj); err != nil {
		panic(err)
	}
}