iOS 屏幕实时共享功能实践（内附详细代码）

很多人对屏幕共享的印象还只停留在 PC 端做 PPT 汇报的场景中，但事实上，今天的屏幕共享早已跨界出圈了。比如一个大家很熟悉的场景 —— 游戏直播，主播就需要将自己的画面以“屏幕共享”的形式展示给观众，并且对实时性、流畅性的要求非常高。

对于很多手游主播来说，目前比较常见的做法是，通过借助 PC 端的中转将手机游戏画面进行直播分享；而实际上，通过调用融云屏幕共享 SDK，直接在手机端就可以拥有屏幕实时共享的能力。

本文就将主要围绕 iOS 屏幕共享问题展开讨论，一起了解 iOS ReplayKit 框架的发展过程，各个阶段的功能演变，以及结合融云屏幕共享 SDK 实现相应功能的代码和思路。

01 ReplayKit 发展史

iOS 端屏幕录制 ReplayKit 是从 iOS9 开始出现的。

iOS9

WWDC15 初次提供 ReplayKit 框架，它的初期出现主要用于录制视频，存于相册。

iOS9 开始录制和停止录制两个 API 有很大的局限性：

• 只能获取系统生成好的 MP4 文件，且不能直接获取，需要先保存到相册，再从相册获取；

• 不可以获取源数据，也就是 pcm 和 yuv 数据；

• 给开发者的权限低，不能录制其他 APP，且退出后台就不会录制了，只能录制当前 APP 画面。

可控行为在于：

• 停止录制可弹出一个视频预览窗口，能进行保存或取消或分享该视频文件；

• 录制完成后可以进行查看、编辑，或者通过指定方式分享。

开始录制视频的 API 如下所示。

/*!
 Deprecated. Use startRecordingWithHandler: instead.

 @abstract Starts app recording with a completion handler. Note that before recording actually starts, the user may be prompted with UI to confirm recording.
 @param microphoneEnabled Determines whether the microphone input should be included in the recorded movie audio.
 @discussion handler Called after user interactions are complete. Will be passed an optional NSError in the RPRecordingErrorDomain domain if there was an issue starting the recording.
 */
[[RPScreenRecorder sharedRecorder] startRecordingWithMicrophoneEnabled:YES handler:^(NSError * _Nullable error) {
        if (error) {
            //TODO.....
        }
}];

调用开始录屏的时候，系统会弹出一个弹窗，需要用户进行确认后才能正常录制。

（图1  启动系统录制弹窗）
 

停止录制视频的 API 如下所示。

/*! @abstract Stops app recording with a completion handler.
 @discussion handler Called when the movie is ready. Will return an instance of RPPreviewViewController on success which should be presented using [UIViewController presentViewController:animated:completion:]. Will be passed an optional NSError in the RPRecordingErrorDomain domain if there was an issue stopping the recording.
 */
[[RPScreenRecorder sharedRecorder] stopRecordingWithHandler:^(RPPreviewViewController *previewViewController, NSError *  error){
            [self presentViewController:previewViewController animated:YES completion:^{
                //TODO.....
            }];
}];

（图2  录制屏幕完成系统页面）

iOS10

经过 WWDC16 发布，苹果对 ReplayKit 进行了升级，开放了源数据获取途径，增加了两个 Extension 的 Target。具体情况包括：

• 新增 UI 和 Upload 两个 Extension 的 Target；

• 增加开发者权限，允许用户登录到服务并设立了直播、源数据的操作；

• 只能通过扩展区录制屏幕，不仅可以录制自己的 APP，还可以录制其他 APP；

• 只能录制 APP 屏幕，不能录制 iOS 系统屏幕。

创建 Extension 的方法如下图所示。

（图3  创建 Extension 图示）

UI Extension

/*
这俩API可以理解为弹窗触发的事件回调函数；
*/
- (void)userDidFinishSetup {
  //触发  Host App 的RPBroadcastActivityViewControllerDelegate
}

- (void)userDidCancelSetup {
    //触发  Host App 的RPBroadcastActivityViewControllerDelegate
}

Upload Extension

- (void)broadcastStartedWithSetupInfo:(NSDictionary<NSString *,NSObject *> *)setupInfo {
    // User has requested to start the broadcast. Setup info from the UI extension can be supplied but optional.
  //这里主要就是做一些初始化的行为操作
}

- (void)broadcastPaused {
    // User has requested to pause the broadcast. Samples will stop being delivered.
  //接收系统暂停信号
}

- (void)broadcastResumed {
    // User has requested to resume the broadcast. Samples delivery will resume.
  //接收系统恢复信号
}

- (void)broadcastFinished {
    // User has requested to finish the broadcast.
  //接收系统完成信号
}

 //这里就是此次更新最炸的点，我们可以拿到系统源数据，而且系统还分了三类，分别为视频帧、App内声音、麦克风
- (void)processSampleBuffer:(CMSampleBufferRef)sampleBuffer withType:(RPSampleBufferType)sampleBufferType {
   
    switch (sampleBufferType) {
        case RPSampleBufferTypeVideo:
            // Handle video sample buffer
            break;
        case RPSampleBufferTypeAudioApp:
            // Handle audio sample buffer for app audio
            break;
        case RPSampleBufferTypeAudioMic:
            // Handle audio sample buffer for mic audio
            break;
            
        default:
            break;
    }
}

Host APP

RPBroadcastControllerDelegate
//start
if (![RPScreenRecorder sharedRecorder].isRecording) {
      [RPBroadcastActivityViewController loadBroadcastActivityViewControllerWithHandler:^(RPBroadcastActivityViewController * _Nullable broadcastActivityViewController, NSError * _Nullable error) {
          if (error) {
              NSLog(@"RPBroadcast err %@", [error localizedDescription]);
          }
          broadcastActivityViewController.delegate = self; /*RPBroadcastActivityViewControllerDelegate*/
          [self presentViewController:broadcastActivityViewController animated:YES completion:nil];
      }];
  }

#pragma mark- RPBroadcastActivityViewControllerDelegate
- (void)broadcastActivityViewController:(RPBroadcastActivityViewController *)broadcastActivityViewController didFinishWithBroadcastController:(RPBroadcastController *)broadcastController error:(NSError *)error {
  if （error） {
    //TODO:
    NSLog(@"broadcastActivityViewController:%@",error.localizedDescription);
    return;
  }
  
   [broadcastController startBroadcastWithHandler:^(NSError * _Nullable error) {
        if (!error) {
            NSLog(@"success");
        } else {
            NSLog(@"startBroadcast:%@",error.localizedDescription);
        }
    }];
}

#pragma mark- RPBroadcastControllerDelegate
- (void)broadcastController:(RPBroadcastController *)broadcastController didFinishWithError:(nullable NSError *)error{
    NSLog(@"didFinishWithError: %@", error);
}
- (void)broadcastController:(RPBroadcastController *)broadcastController didUpdateServiceInfo:(NSDictionary <NSString *, NSObject <NSCoding> *> *)serviceInf {
    NSLog(@"didUpdateServiceInfo: %@", serviceInf);
}

iOS11

经过 WWDC17，苹果对 ReplayKit2 进行了再次升级，新增了 APP 外数据获取，可以直接在 Host App 中获取，具体包括：

• 可以直接在 Host APP 中处理录制的 APP 屏幕数据；

• 可以录制 iOS 系统的屏幕数据，但是需要通过控制中心手动开启。

启动 APP 屏幕录制

[[RPScreenRecorder sharedRecorder] startCaptureWithHandler:^(CMSampleBufferRef  _Nonnull sampleBuffer, RPSampleBufferType bufferType, NSError * _Nullable error) {
    [self.videoOutputStream write:sampleBuffer error:nil];
} completionHandler:^(NSError * _Nullable error) {
    NSLog(@"startCaptureWithHandler:%@",error.localizedDescription);
}];

停止 APP 屏幕录制

[[RPScreenRecorder sharedRecorder] stopCaptureWithHandler:^(NSError * _Nullable error) {
        [self.assetWriter finishWritingWithCompletionHandler:^{
            //TODO
        }];
}];

iOS12

苹果在 WWDC18 上针对 ReplayKit 更新，新增了 RPSystemBroadcastPickerView，类用于在 APP 内可启动系统录制，极大地简化了屏幕录制的流程。

if (@available(iOS 12.0, *)) {
        self.systemBroadcastPickerView = [[RPSystemBroadcastPickerView alloc] initWithFrame:CGRectMake(0, 0, 50, 80)];
        self.systemBroadcastPickerView.preferredExtension = ScreenShareBuildID;
        self.systemBroadcastPickerView.showsMicrophoneButton = NO;
        self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:self.systemBroadcastPickerView];
} else {
    // Fallback on earlier versions
}

02 融云 RongRTCReplayKitExt

为减轻开发者的集成负担，融云专门打造了 RongRTCReplayKitExt 库，以服务于屏幕共享业务。

设计思路

Upload Extension

SampleHandler 进行数据的接收、RCRTCReplayKitEngine 初始化配置 ；

RCRTCReplayKitEngine 初始化 socket 通讯、处理YUV数据转i420、控制内存峰值。

App

原有发布流程：

IM 连接–加入房间–发布资源（RCRTCScreenShareOutputStream）；

内部做 socket 初始化、实现协议接收处理过的数据、推流 。

（图4  设计思路流程图）

代码示例

Upload extension

#import "SampleHandler.h"
#import <RongRTCReplayKitExt/RongRTCReplayKitExt.h>

static NSString *const ScreenShareGroupID = @"group.cn.rongcloud.rtcquickdemo.screenshare";

@interface SampleHandler ()<RongRTCReplayKitExtDelegate>
@end

@implementation SampleHandler

- (void)broadcastStartedWithSetupInfo:(NSDictionary<NSString *, NSObject *> *)setupInfo {
    // User has requested to start the broadcast. Setup info from the UI extension can be supplied but optional.
    [[RCRTCReplayKitEngine sharedInstance] setupWithAppGroup:ScreenShareGroupID delegate:self];
}

- (void)broadcastPaused {
    // User has requested to pause the broadcast. Samples will stop being delivered.
}

- (void)broadcastResumed {
    // User has requested to resume the broadcast. Samples delivery will resume.
}

- (void)broadcastFinished {
    [[RCRTCReplayKitEngine sharedInstance] broadcastFinished];
}

- (void)processSampleBuffer:(CMSampleBufferRef)sampleBuffer withType:(RPSampleBufferType)sampleBufferType  API_AVAILABLE(ios(10.0)) {
    switch (sampleBufferType) {
        case RPSampleBufferTypeVideo:
            [[RCRTCReplayKitEngine sharedInstance] sendSampleBuffer:sampleBuffer withType:RPSampleBufferTypeVideo];
            break;
        case RPSampleBufferTypeAudioApp:
            // Handle audio sample buffer for app audio
            break;
        case RPSampleBufferTypeAudioMic:
            // Handle audio sample buffer for mic audio
            break;

        default:
            break;
    }
}

#pragma mark - RongRTCReplayKitExtDelegate
-(void)broadcastFinished:(RCRTCReplayKitEngine *)broadcast reason:(RongRTCReplayKitExtReason)reason {
    NSString *tip = @"";
    switch (reason) {
        case RongRTCReplayKitExtReasonRequestedByMain:
            tip = @"屏幕共享已结束......";
            break;
        case RongRTCReplayKitExtReasonDisconnected:
            tip = @"应用断开.....";
            break;
        case RongRTCReplayKitExtReasonVersionMismatch:
            tip = @"集成错误（SDK 版本号不相符合）........";
            break;
    }

    NSError *error = [NSError errorWithDomain:NSStringFromClass(self.class)
                                         code:0
                                     userInfo:@{
                                         NSLocalizedFailureReasonErrorKey:tip
                                     }];
    [self finishBroadcastWithError:error];
}

Host App

- (void)joinRoom {
    RCRTCVideoStreamConfig *videoConfig = [[RCRTCVideoStreamConfig alloc] init];
    videoConfig.videoSizePreset = RCRTCVideoSizePreset720x480;
    videoConfig.videoFps = RCRTCVideoFPS30;
    [[RCRTCEngine sharedInstance].defaultVideoStream setVideoConfig:videoConfig];

    RCRTCRoomConfig *config = [[RCRTCRoomConfig alloc] init];
    config.roomType = RCRTCRoomTypeNormal;

    [self.engine enableSpeaker:YES];

    __weak typeof(self) weakSelf = self;
    [self.engine joinRoom:self.roomId
                   config:config
               completion:^(RCRTCRoom *_Nullable room, RCRTCCode code) {
                   __strong typeof(weakSelf) strongSelf = weakSelf;
                   if (code == RCRTCCodeSuccess) {
                       self.room = room;
                       room.delegate = self;
                       [self publishScreenStream];
                   } else {
                       [UIAlertController alertWithString:@"加入房间失败" inCurrentViewController:strongSelf];
                   }
               }];
}

- (void)publishScreenStream {
    self.videoOutputStream = [[RCRTCScreenShareOutputStream alloc] initWithAppGroup:ScreenShareGroupID];

    RCRTCVideoStreamConfig *videoConfig = self.videoOutputStream.videoConfig;
    videoConfig.videoSizePreset = RCRTCVideoSizePreset1280x720;
    videoConfig.videoFps = RCRTCVideoFPS24;
    [self.videoOutputStream setVideoConfig:videoConfig];
    
    [self.room.localUser publishStream:self.videoOutputStream
                            completion:^(BOOL isSuccess, RCRTCCode desc) {
                                if (isSuccess) {
                                    NSLog(@"发布自定义流成功");
                                } else {
                                    NSLog(@"发布自定义流失败%@", [NSString stringWithFormat:@"订阅远端流失败:%ld", (long) desc]);
                                }
                            }];
}

03 一些注意事项

第一，ReplayKit2 内存不能超过 50MB，一旦超过峰值系统会进行强制回收，所以在 Extension 里面处理数据需要格外注意内存释放。

第二，进程之前通讯，如果是以 CFDefaultcenter 不能携带参数，只能发送消息；如果需要携带参数，必须做本地文件缓存。这里需要注意的一个问题是，在 debug 模式下运行可以打印出数据，在 release 下获取不到本地文件数据，具体实现可参见 Github 中的攻略。

最后想小小吐槽一下：非正常结束录屏时，系统往往会出现弹窗，且这个弹窗无法删除，只能重启设备 —— 这应该算是 iOS 系统一个比较恼人的 BUG 了。