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Share the Screen

Last updated 2022/04/11 12:29:19

Introduction

Screen sharing enables the host of an interactive live streaming broadcast or video call to display what is on their screen to other users in the channel. This technology has many obvious advantages for communicating information, particularly in the following scenarios:

During video conferencing, the speaker can share a local image, web page, or full presentation with other participants.
For online instruction, the teacher can share slides or notes with students.

Implementations for v3.7.0 and later

This section describes how to implement screen sharing using the Android SDK v3.7.0 and later.

Before you begin, ensure that you understand how to start a video call or start interactive video streaming. For details, see Start a Video Call or Start Interactive Video Streaming.

1. Integrate the AgoraScreenShareExtension

Copy the AgoraScreenShareExtension.aar file of the SDK to the /app/libs/ directory.
Add the following line in the dependencies node in the /app/build.gradle file to support importing files in the AAR format.
```
 implementation fileTree(dir: "libs", include: ["*.jar","*.aar"])
```

2. Call the API

Call startScreenCapture to start screen sharing.

Sample project

Agora provides an open-source sample project on GitHub for your reference.

API reference

Some restrictions and cautions exist for using the screen sharing feature, and charges can apply. Agora recommends that you read the following API references before calling the API:

Implementations earlier than v3.7.0

This section describes how to implement screen sharing using the Android SDK earlier than v3.7.0.

Before you begin, ensure that you understand how to start a video call or start interactive video streaming. For details, see Start a Video Call or Start Interactive Video Streaming.

The Agora SDK does not provide any method for screen share on Android. Therefore, You need to implement this function using the native screen-capture APIs provided by Android, and the custom video-source APIs provided by Agora.

Use android.media.projection and android.hardware.display.VirtualDisplay to get and pass the screen-capture data.
Create an OpenGL ES environment. Create a SurfaceView object and pass the object to VirtualDisplay, which works as the recipient of the screen-capture data.
You can get the screen-capture data from the callbacks of SurfaceView. Use either the Push mode or mediaIO mode to push the screen-capture data to the SDK. For details, see Custom Video Source and Renderer.

Data transfer

The following diagram shows how data is transferred during screen sharing on Android:

Sample code

The code samples provided in this section use MediaProjection and VirtualDisplay APIs provided by Android and have the following Android/API version requirements:

The Android version must be Lollipop or higher.
To use MediaProjection APIs, the Android API level must be 21 or higher.
To use VirtualDisplay APIs, the Android API level must be 19 or higher.

For detailed usage and considerations, see the Android documentation MediaProjection and VirtualDisplay.

Implement IVideoSource and IVideoFrameConsumer, and rewrite the callbacks in IVideoSource.

 // Implements the IVideoSource interface
 public class ExternalVideoInputManager implements IVideoSource {
 ...
     // Gets the IVideoFrameConsumer object when initializing the video source
     @Override
     public boolean onInitialize(IVideoFrameConsumer consumer) {
         mConsumer = consumer;
         return true;
     }

     @Override
     public boolean onStart() {
         return true;
     }

     @Override
     public void onStop() {

     }
     // Sets IVideoFrameConsumer as null when IVideoFrameConsumer is released by the media engine
     @Override
     public void onDispose() {
         Log.e(TAG, "SwitchExternalVideo-onDispose");
         mConsumer = null;
     }

     @Override
     public int getBufferType() {
         return TEXTURE.intValue();
     }

     @Override
     public int getCaptureType() {
         return CAMERA;
     }

     @Override
     public int getContentHint() {
         return MediaIO.ContentHint.NONE.intValue();
     }
  ...
 }

 // Implements IVideoFrameConsumer
 private volatile IVideoFrameConsumer mConsumer;

Set the custom video source before joining a channel.

 // Sets the input thread of the custom video source
 // In the sample project, we use the class in the open-source grafika project, which encapsulates the graphics architecture of Android. For details, see https://source.android.com/devices/graphics/architecture
 // For detailed implementation of EglCore, GlUtil, EGLContext, and ProgramTextureOES, see https://github.com/google/grafika
 // The GLThreadContext class contains EglCore, EGLContext, and ProgramTextureOES
 private void prepare() {
             // Creates an OpenEL ES environment based on EglCore
             mEglCore = new EglCore();
             mEglSurface = mEglCore.createOffscreenSurface(1, 1);
             mEglCore.makeCurrent(mEglSurface);
             // Creates an EGL texture object based on GlUtil
             mTextureId = GlUtil.createTextureObject(GLES11Ext.GL_TEXTURE_EXTERNAL_OES);
             // Creates a SurfaceTexture object based on EGL texture
             mSurfaceTexture = new SurfaceTexture(mTextureId);
             // Surface a Surface object based on SurfaceTexture
             mSurface = new Surface(mSurfaceTexture);
             // Pass EGLCore, EGL context, and ProgramTextureOES to GLThreadContext as its members
             mThreadContext = new GLThreadContext();
             mThreadContext.eglCore = mEglCore;
             mThreadContext.context = mEglCore.getEGLContext();
             mThreadContext.program = new ProgramTextureOES();

             // Sets the custom video source
             ENGINE.setVideoSource(ExternalVideoInputManager.this);
         }

Create an intent based on MediaProjection, and pass the intent to the startActivityForResult() method to start capturing screen data.

 private class VideoInputServiceConnection implements ServiceConnection {
     @Override
     public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
         mService = (IExternalVideoInputService) iBinder;
 // Starts capturing screen data. Ensure that your Android version must be Lollipop or higher.
 if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
                 // Instantiates a MediaProjectionManager object
                 MediaProjectionManager mpm = (MediaProjectionManager)
                         getContext().getSystemService(Context.MEDIA_PROJECTION_SERVICE);
                 // Creates an intent
                 Intent intent = mpm.createScreenCaptureIntent();
                 // Starts screen capturing
                 startActivityForResult(intent, PROJECTION_REQ_CODE);
             }

Get the screen-capture data information from the activity result.

 // Gets the intent of the data information from activity result
  @Override
     public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
         super.onActivityResult(requestCode, resultCode, data);
         if (requestCode == PROJECTION_REQ_CODE && resultCode == RESULT_OK) {
             ...
                 // Sets the custom video source as the screen-capture data
                 mService.setExternalVideoInput(ExternalVideoInputManager.TYPE_SCREEN_SHARE, data);
             }
             catch (RemoteException e) {
                 e.printStackTrace();
             }
         }
     }

The implementation of setExternalVideoInput(int type, Intent intent) is as follows:

 // Gets the parameters of the screen-capture data from intent
 boolean setExternalVideoInput(int type, Intent intent) {

         if (mCurInputType == type && mCurVideoInput != null
                 && mCurVideoInput.isRunning()) {
             return false;
         }

         IExternalVideoInput input;
         switch (type) {
             ...
             case TYPE_SCREEN_SHARE:
                 // Gets the screen-capture data from the intent of MediaProjection
                 int width = intent.getIntExtra(FLAG_SCREEN_WIDTH, DEFAULT_SCREEN_WIDTH);
                 int height = intent.getIntExtra(FLAG_SCREEN_HEIGHT, DEFAULT_SCREEN_HEIGHT);
                 int dpi = intent.getIntExtra(FLAG_SCREEN_DPI, DEFAULT_SCREEN_DPI);
                 int fps = intent.getIntExtra(FLAG_FRAME_RATE, DEFAULT_FRAME_RATE);
                 Log.i(TAG, "ScreenShare:" + width + "|" + height + "|" + dpi + "|" + fps);
                 // Instantiates a ScreenShareInput class using the screen-capture data
                 input = new ScreenShareInput(context, width, height, dpi, fps, intent);
                 break;
             default:
                 input = null;
         }
         // Sets the captured video data as the ScreenShareInput object, and creates an input thread for external video data
         setExternalVideoInput(input);
         mCurInputType = type;
         return true;
     }

During the initialization of the input thread of the external video data, create a VirtualDisplay object with MediaProjection, and render VirtualDisplay on SurfaceView.

 public void onVideoInitialized(Surface target) {
         MediaProjectionManager pm = (MediaProjectionManager)
                 mContext.getSystemService(Context.MEDIA_PROJECTION_SERVICE);
         mMediaProjection = pm.getMediaProjection(Activity.RESULT_OK, mIntent);

         if (mMediaProjection == null) {
             Log.e(TAG, "media projection start failed");
             return;
         }
         // Creates VirtualDisplay with MediaProjection, and render VirtualDisplay on SurfaceView
         mVirtualDisplay = mMediaProjection.createVirtualDisplay(
                 VIRTUAL_DISPLAY_NAME, mSurfaceWidth, mSurfaceHeight, mScreenDpi,
                 DisplayManager.VIRTUAL_DISPLAY_FLAG_PUBLIC, target,
                 null, null);
     }

Use SurfaceView as the custom video source. After the user joins the channel, the custom video module gets the screen-capture data using consumeTextureFrame in ExternalVideoInputThread and passes the data to the SDK.

 public void run() {
                 ...
                 // Calls updateTexImage() to update the data to the texture object of OpenGL ES
                 // Calls getTransformMatrix() to transform the texture matrix
                  try {
                  mSurfaceTexture.updateTexImage();
                  mSurfaceTexture.getTransformMatrix(mTransform);
                       }
                  catch (Exception e) {
                  e.printStackTrace();
                  }

                 // Gets the screen-capture data from onFrameAvailable. onFrameAvailable is a rewrite of ScreenShareInput, which gets information such as the texture ID and transform information
                 // No need to render the screen-capture data on the local view
                 if (mCurVideoInput != null) {
                     mCurVideoInput.onFrameAvailable(mThreadContext, mTextureId, mTransform);
                 }

                 mEglCore.makeCurrent(mEglSurface);
                 GLES20.glViewport(0, 0, mVideoWidth, mVideoHeight);

                 if (mConsumer != null) {
                     Log.e(TAG, "SDK encoding->width:" + mVideoWidth + ",height:" + mVideoHeight);
                     // Calls consumeTextureFrame to pass the video data to the SDK
                     mConsumer.consumeTextureFrame(mTextureId,
                             TEXTURE_OES.intValue(),
                             mVideoWidth, mVideoHeight, 0,
                             System.currentTimeMillis(), mTransform);
                 }

                 // Waits for the next frame
                 waitForNextFrame();
                 ...
         }

Sample project

Agora provides an open-source sample project on GitHub to show how to switch the video between screen sharing and the camera.

Currently, the Agora RTC Native SDK supports creating only one RtcEngine instance per app. You need multi-processing to send video from screen sharing and the local camera at the same time.

Implementation

You need to create separate processes for screen sharing and video captured by the local camera. Both processes use the following methods to send video data to the SDK:

Local-camera process: Implemented with joinChannel. This process is often the main process and communicates with the screen sharing process via AIDL (Android Interface Definition Language). See Android documentation to learn more about AIDL.
Screen sharing process: Implemented with MediaProjection, VirtualDisplay, and custom video capture. The screen sharing process creates an RtcEngine object and uses the object to create and join a channel for screen sharing.

The users of both processes must join the same channel. After joining a channel, a user subscribes to the audio and video streams of all other users in the channel by default, thus incurring all associated usage costs. Because the screen sharing process is only used to publish the screen sharing stream, you can call muteAllRemoteAudioStreams(true) and muteAllRemoteVideoStreams(true) to mute remote audio and video streams.

Sample code

The following sample code uses multi-processing to send the video from the screen sharing video and locally captured video. AIDL is used to communicate between the processes.

Configure android:process in AndroidManifest.xml for the components.

 <application>
     <activity
         android:name=".impl.ScreenCapture$ScreenCaptureAssistantActivity"
         android:process=":screensharingsvc"
         android:screenOrientation="fullUser"
         android:theme="@android:style/Theme.Translucent" />
     <service
         android:name=".impl.ScreenSharingService"
         android:process=":screensharingsvc">
         <intent-filter>
             <action android:name="android.intent.action.screenshare" />
         </intent-filter>
     </service>
  </application>

Create an AIDL interface, which includes methods to communicate between processes.

 // Includes methods to manage the screen sharing process
 // IScreenSharing.aidl
 package io.agora.rtc.ss.aidl;

 import io.agora.rtc.ss.aidl.INotification;

 interface IScreenSharing {
     void registerCallback(INotification callback);
     void unregisterCallback(INotification callback);
     void startShare();
     void stopShare();
     void renewToken(String token);
 }

 // Includes callbacks to receive notifications from the screen sharing process
 // INotification.aidl
 package io.agora.rtc.ss.aidl;

 interface INotification {
     void onError(int error);
     void onTokenWillExpire();
 }

Implement the screen sharing process. Screen sharing is implemented with MediaProjection, VirtualDisplay, and custom video source. The screen sharing process creates an RtcEngine object and uses the object to create and join a channel for screen sharing.

 // Define the ScreenSharingClient object
 public class ScreenSharingClient {
     private static final String TAG = ScreenSharingClient.class.getSimpleName();
     private static IScreenSharing mScreenShareSvc;
     private IStateListener mStateListener;
     private static volatile ScreenSharingClient mInstance;

     public static ScreenSharingClient getInstance() {
         if (mInstance == null) {
             synchronized (ScreenSharingClient.class) {
                 if (mInstance == null) {
                     mInstance = new ScreenSharingClient();
                 }
             }
         }

         return mInstance;
     }

 // Start screen sharing
 public void start(Context context, String appId, String token, String channelName, int uid, VideoEncoderConfiguration vec) {
         if (mScreenShareSvc == null) {
             Intent intent = new Intent(context, ScreenSharingService.class);
             intent.putExtra(Constant.APP_ID, appId);
             intent.putExtra(Constant.ACCESS_TOKEN, token);
             intent.putExtra(Constant.CHANNEL_NAME, channelName);
             intent.putExtra(Constant.UID, uid);
             intent.putExtra(Constant.WIDTH, vec.dimensions.width);
             intent.putExtra(Constant.HEIGHT, vec.dimensions.height);
             intent.putExtra(Constant.FRAME_RATE, vec.frameRate);
             intent.putExtra(Constant.BITRATE, vec.bitrate);
             intent.putExtra(Constant.ORIENTATION_MODE, vec.orientationMode.getValue());
             context.bindService(intent, mScreenShareConn, Context.BIND_AUTO_CREATE);
         } else {
             try {
                 mScreenShareSvc.startShare();
             } catch (RemoteException e) {
                 e.printStackTrace();
                 Log.e(TAG, Log.getStackTraceString(e));
             }
         }

     }

 // Stop screen sharing
 public void stop(Context context) {
         if (mScreenShareSvc != null) {
             try {
                 mScreenShareSvc.stopShare();
                 mScreenShareSvc.unregisterCallback(mNotification);
             } catch (RemoteException e) {
                 e.printStackTrace();
                 Log.e(TAG, Log.getStackTraceString(e));
             } finally {
                 mScreenShareSvc = null;
             }
         }
         context.unbindService(mScreenShareConn);
     }
 ...
 }

After binding the screen sharing service, the screen sharing process creates an RtcEngine object and joins the channel for screen sharing.

     @Override
     public IBinder onBind(Intent intent) {
         // Creates a RtcEngine object
         setUpEngine(intent);
         // Set video encoding configurations
         setUpVideoConfig(intent);
         // Join the channel
         joinChannel(intent);
         return mBinder;
     }

When creating the RtcEngine object in the screen sharing process, perform the following configurations:

 // Mute all audio streams
 mRtcEngine.muteAllRemoteAudioStreams(true);
 // Mute all video streams
 mRtcEngine.muteAllRemoteVideoStreams(true);
 // Disable the audio module
 mRtcEngine.disableAudio();

Implement the local-camera process and the code logic to start the screen sharing process.

 public class MultiProcess extends BaseFragment implements View.OnClickListener
 {
     private static final String TAG = MultiProcess.class.getSimpleName();
     // Define the uid for the screen sharing process
     private static final Integer SCREEN_SHARE_UID = 10000;
     ...
     @Override
     public void onActivityCreated(@Nullable Bundle savedInstanceState)
     {
         super.onActivityCreated(savedInstanceState);
         Context context = getContext();
         if (context == null)
         {
             return;
         }
         try
         {
             // Create an RtcEngine instance
             engine = RtcEngine.create(context.getApplicationContext(), getString(R.string.agora_app_id), iRtcEngineEventHandler);
             // Initialize the screen sharing process
             mSSClient = ScreenSharingClient.getInstance();
             mSSClient.setListener(mListener);
         }
         catch (Exception e)
         {
             e.printStackTrace();
             getActivity().onBackPressed();
         }
     }
     ...
             // Run the screen sharing process and send information such as App ID and channel ID to the screen sharing process
             else if (v.getId() == R.id.screenShare){
             String channelId = et_channel.getText().toString();
             if (!isSharing) {
                 mSSClient.start(getContext(), getResources().getString(R.string.agora_app_id), null,
                         channelId, SCREEN_SHARE_UID, new VideoEncoderConfiguration(
                                 VD_640x360,
                                 FRAME_RATE_FPS_15,
                                 STANDARD_BITRATE,
                                 ORIENTATION_MODE_ADAPTIVE
                         ));
                 screenShare.setText(getResources().getString(R.string.stop));
                 isSharing = true;
             } else {
                 mSSClient.stop(getContext());
                 screenShare.setText(getResources().getString(R.string.screenshare));
                 isSharing = false;
             }
         }
       ...
         // Create a view for local preview
         SurfaceView surfaceView = RtcEngine.CreateRendererView(context);
         if(fl_local.getChildCount() > 0)
         {
             fl_local.removeAllViews();
         }
       ...
         // Join channel
         int res = engine.joinChannel(accessToken, channelId, "Extra Optional Data", 0);
         if (res != 0)
         {
             showAlert(RtcEngine.getErrorDescription(Math.abs(res)));
             return;
         }
         join.setEnabled(false);
     }

Sample project

Agora provides an open-source sample project on GitHub to show how to send video from both screen sharing and the camera by using dual processes.

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Share the Screen

Introduction

Share a screen

Implementations for v3.7.0 and later

1. Integrate the AgoraScreenShareExtension

2. Call the API

Sample project

API reference

Implementations earlier than v3.7.0

Data transfer

Sample code

Sample project

Send video streams from screen sharing and local camera

Implementation

Sample code

Sample project