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，明天的屏幕共享早已跨界出圈了。比方一个大家很相熟的场景 —— 游戏直播，主播就须要将本人的画面以“屏幕共享”的模式展现给观众，并且对实时性、流畅性的要求十分高。
对于很多手游主播来说，目前比拟常见的做法是，通过借助 PC 端的直达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，间接在手机端就能够领有屏幕实时共享的能力。
本文就将次要围绕 iOS 屏幕共享问题展开讨论，一起理解 iOS ReplayKit 框架的倒退过程，各个阶段的性能演变，以及联合融云屏幕共享 SDK 实现相应性能的代码和思路。
01 ReplayKit 发展史
iOS 端屏幕录制 ReplayKit 是从 iOS9 开始呈现的。
iOS9
WWDC15 首次提供 ReplayKit 框架，它的初期呈现次要用于录制视频，存于相册。
iOS9 开始录制和进行录制两个 API 有很大的局限性：
只能获取系统生成好的 MP4 文件，且不能间接获取，须要先保留到相册，再从相册获取；
不能够获取源数据，也就是 pcm 和 yuv 数据；
给开发者的权限低，不能录制其余 APP，且退出后盾就不会录制了，只能录制以后 APP 画面。
可控行为在于：
进行录制可弹出一个视频预览窗口，能进行保留或勾销或分享该视频文件；
录制实现后能够进行查看、编辑，或者通过指定形式分享。
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，零碎会弹出一个弹窗，须要用户进行确认后能力失常录制。
进行录制视频的 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..... }];}];iOS10
通过 WWDC16 公布，苹果对 ReplayKit 进行了降级，凋谢了源数据获取路径，减少了两个 Extension 的 Target。具体情况包含：
新增 UI 和 Upload 两个 Extension 的 Target；
减少开发者权限，容许用户登录到服务并设立了直播、源数据的操作；
只能通过扩大区录制屏幕，不仅能够录制本人的 APP，还能够录制其余 APP；
只能录制 APP 屏幕，不能录制 iOS 零碎屏幕。
创立 Extension 的办法如下图所示。
UI Extension
/*这俩API能够了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. //这里次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. //接管零碎暂停信号}- (void)broadcastResumed { // User has requested to resume the broadcast. Samples delivery will resume. //接管零碎复原信号}- (void)broadcastFinished { // User has requested to finish the broadcast. //接管零碎实现信号} //这里就是此次更新最炸的点，咱们能够拿到零碎源数据，而且零碎还分了三类，别离为视频帧、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//startif (![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
通过 WWDC17，苹果对 ReplayKit2 进行了再次降级，新增了 APP 外数据获取，能够间接在 Host App 中获取，具体包含：
能够间接在 Host APP 中解决录制的 APP 屏幕数据；
能够录制 iOS 零碎的屏幕数据，然而须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);}];进行 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 内可启动零碎录制，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
为加重开发者的集成累赘，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 进行数据的接管、RCRTCReplayKitEngine 初始化配置 ；
RCRTCReplayKitEngine 初始化 socket 通信、解决YUV数据转i420、管制内存峰值。
App
原有公布流程：
IM 连贯--退出房间--公布资源（RCRTCScreenShareOutputStream）；
外部做 socket 初始化、实现协定接管解决过的数据、推流。
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 = @"屏幕共享已完结......"; break; case RongRTCReplayKitExtReasonDisconnected: tip = @"利用断开....."; break; case RongRTCReplayKitExtReasonVersionMismatch: tip = @"集成谬误（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:@"退出房间失败" 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(@"公布自定义流胜利"); } else { NSLog(@"公布自定义流失败%@", [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，一旦超过峰值零碎会进行强制回收，所以在 Extension 外面解决数据须要分外留神内存开释。
第二，过程之前通信，如果是以 CFDefaultcenter 不能携带参数，只能发送音讯；如果须要携带参数，必须做本地文件缓存。这里须要留神的一个问题是，在 debug 模式下运行能够打印出数据，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。
最初想小小吐槽一下：非正常完结录屏时，零碎往往会呈现弹窗，且这个弹窗无奈删除，只能重启设施 —— 这应该算是 iOS 零碎一个比拟宜人的 BUG 了。