WebRTC安卓端没有官方教程，甚至连API文档都没有。这是一件奇怪的事，毕竟WebRTC是Google开发的。目前官方文档和Demo都只有web端的，虽然写得简单易懂，整体用法也和安卓端相同，但是具体细节还是有巨大的差异。

当然，仔细找Google和Github上还是能找到一些不错的教程，我这里将它们结合一下，组成一个完整的入门教程，并带有可运行Demo.

首先介绍一些基本概念
RTC(Real Time Communication): 实时通信
WebRTC: 基于web的实时通信
Signaling: 信令, 一些描述媒体或网络的字符串
SDP(Session Description Protocol): 会话描述协议, 主要描述媒体信息
ICE(Interactive Connectivity Establishment): 交互式连接建立
STUN(Session Traversal Utilities for NAT): NAT会话穿透工具
TURN(Traversal Using Relays around NAT): 中继穿透NAT

接下来是使用方法

添加WebRTC库

在module的build.gradle中添加依赖，这个是官方打包的最新版本（201901）。当然你也可以 自己构建.

dependencies {
    ...
    implementation 'org.webrtc:google-webrtc:1.0.26131'
}

添加权限

    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.RECORD_AUDIO" />

注意Android6.0以上需要到设置里开启相机和麦克风权限。因为跟主题无关, 所以这里没加申请权限代码.

添加SurfaceViewRenderer

它是SurfaceView的子类

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cc.rome753.wat.MainActivity">

    <org.webrtc.SurfaceViewRenderer
        android:id="@+id/localView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

使用相机

主要步骤如下

1. 创建PeerConnectionFactory
2. 创建并启动VideoCapturer
3. 用PeerConnectionFactory创建VideoSource
4. 用PeerConnectionFactory和VideoSource创建VideoTrack
5. 初始化视频控件SurfaceViewRenderer
6. 将VideoTrack展示到SurfaceViewRenderer中

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // create PeerConnectionFactory
        PeerConnectionFactory.InitializationOptions initializationOptions =
                PeerConnectionFactory.InitializationOptions.builder(this).createInitializationOptions();
        PeerConnectionFactory.initialize(initializationOptions);
        PeerConnectionFactory peerConnectionFactory = PeerConnectionFactory.builder().createPeerConnectionFactory();

        // create AudioSource
        AudioSource audioSource = peerConnectionFactory.createAudioSource(new MediaConstraints());
        AudioTrack audioTrack = peerConnectionFactory.createAudioTrack("101", audioSource);

        EglBase.Context eglBaseContext = EglBase.create().getEglBaseContext();

        SurfaceTextureHelper surfaceTextureHelper = SurfaceTextureHelper.create("CaptureThread", eglBaseContext);
        // create VideoCapturer
        VideoCapturer videoCapturer = createCameraCapturer();
        VideoSource videoSource = peerConnectionFactory.createVideoSource(videoCapturer.isScreencast());
        videoCapturer.initialize(surfaceTextureHelper, getApplicationContext(), videoSource.getCapturerObserver());
        videoCapturer.startCapture(480, 640, 30);

        SurfaceViewRenderer localView = findViewById(R.id.localView);
        localView.setMirror(true);
        localView.init(eglBaseContext, null);

        // create VideoTrack
        VideoTrack videoTrack = peerConnectionFactory.createVideoTrack("101", videoSource);
        // display in localView
        videoTrack.addSink(localView);
    }

    private VideoCapturer createCameraCapturer() {
        Camera1Enumerator enumerator = new Camera1Enumerator(false);
        final String[] deviceNames = enumerator.getDeviceNames();

        // First, try to find front facing camera
        for (String deviceName : deviceNames) {
            if (enumerator.isFrontFacing(deviceName)) {
                VideoCapturer videoCapturer = enumerator.createCapturer(deviceName, null);

                if (videoCapturer != null) {
                    return videoCapturer;
                }
            }
        }

        // Front facing camera not found, try something else
        for (String deviceName : deviceNames) {
            if (!enumerator.isFrontFacing(deviceName)) {
                VideoCapturer videoCapturer = enumerator.createCapturer(deviceName, null);

                if (videoCapturer != null) {
                    return videoCapturer;
                }
            }
        }

        return null;
    }

}

附录

https://webrtc.org/start/
https://codelabs.developers.google.com/codelabs/webrtc-web/#0
https://developer.mozilla.org/en-US/docs/Web/API/MediaStream
https://vivekc.xyz/getting-started-with-webrtc-for-android-daab1e268ff4
https://www.html5rocks.com/en/tutorials/webrtc/basics/

本项目GitHub地址/step1camera

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