1、iOS直播技术的流程

直播技术的流程大致可以分为几个步骤：数据采集、图像处理（实时滤镜）、视频编码、封包、上传、云端（转码、录制、分发）、直播播放器。

• 数据采集：通过摄像头和麦克风获得实时的音视频数据；
• 图像处理：将数据采集的输入流进行实时滤镜，得到我们美化之后的视频帧；
• 视频编码：编码分为软编码和硬编码。现在一般的编码方式都是H.264，比较新的H.265据说压缩率比较高，但算法也相当要复杂一些，使用还不够广泛。软编码是利用CPU进行编码，硬编码就是使用GPU进行编码，软编码支持现在所有的系统版本，由于苹果在iOS8才开放硬编码的API，故硬编码只支持iOS8以上的系统；
• 封包：现在直播推流中，一般采用的格式是FLV；
• 上传：常用的协议是利用RTMP协议进行推流；
• 云端：进行流的转码、分发和录制；
• 直播播放器：负责拉流、解码、播放。

用一张腾讯云的图来说明上面的流程：

直播技术流程

2、获取系统的授权

直播的第一步就是采集数据，包含视频和音频数据，由于iOS权限的要求，需要先获取访问摄像头和麦克风的权限：

请求获取访问摄像头权限

__weak typeof(self) _self = self;AVAuthorizationStatus status = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];switch (status) {case AVAuthorizationStatusNotDetermined:{// 许可对话没有出现，发起授权许可[AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {if (granted) {dispatch_async(dispatch_get_main_queue(), ^{[_self.session setRunning:YES];});}}];break;}case AVAuthorizationStatusAuthorized:{// 已经开启授权，可继续[_self.session setRunning:YES];break;}case AVAuthorizationStatusDenied:case AVAuthorizationStatusRestricted:// 用户明确地拒绝授权，或者相机设备无法访问break;default:break;}

请求获取访问麦克风权限

AVAuthorizationStatus status = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeAudio];switch (status) {case AVAuthorizationStatusNotDetermined:{[AVCaptureDevice requestAccessForMediaType:AVMediaTypeAudio completionHandler:^(BOOL granted) {}];break;}case AVAuthorizationStatusAuthorized:{break;}case AVAuthorizationStatusDenied:case AVAuthorizationStatusRestricted:break;default:break;}

3、配置采样参数

音频：需要配置码率、采样率；
视频：需要配置视频分辨率、视频的帧率、视频的码率。

4、音视频的录制

音频的录制

 self.taskQueue = dispatch_queue_create("com.1905.live.audioCapture.Queue", NULL);AVAudioSession *session = [AVAudioSession sharedInstance];[session setActive:YES withOptions:kAudioSessionSetActiveFlag_NotifyOthersOnDeactivation error:nil];[[NSNotificationCenter defaultCenter] addObserver: selfselector: @selector(handleRouteChange:)name: AVAudioSessionRouteChangeNotificationobject: session];[[NSNotificationCenter defaultCenter] addObserver: selfselector: @selector(handleInterruption:)name: AVAudioSessionInterruptionNotificationobject: session];NSError *error = nil;[session setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:AVAudioSessionCategoryOptionDefaultToSpeaker | AVAudioSessionCategoryOptionMixWithOthers error:nil];[session setMode:AVAudioSessionModeVideoRecording error:&error];if (![session setActive:YES error:&error]) {[self handleAudioComponentCreationFailure];}AudioComponentDescription acd;acd.componentType = kAudioUnitType_Output;acd.componentSubType = kAudioUnitSubType_RemoteIO;acd.componentManufacturer = kAudioUnitManufacturer_Apple;acd.componentFlags = 0;acd.componentFlagsMask = 0;self.component = AudioComponentFindNext(NULL, &acd);OSStatus status = noErr;status = AudioComponentInstanceNew(self.component, &_componetInstance);if (noErr != status) {[self handleAudioComponentCreationFailure];}UInt32 flagOne = 1;AudioUnitSetProperty(self.componetInstance, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, 1, &flagOne, sizeof(flagOne));AudioStreamBasicDescription desc = {0};desc.mSampleRate = _configuration.audioSampleRate;desc.mFormatID = kAudioFormatLinearPCM;desc.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagsNativeEndian | kAudioFormatFlagIsPacked;desc.mChannelsPerFrame = (UInt32)_configuration.numberOfChannels;desc.mFramesPerPacket = 1;desc.mBitsPerChannel = 16;desc.mBytesPerFrame = desc.mBitsPerChannel / 8 * desc.mChannelsPerFrame;desc.mBytesPerPacket = desc.mBytesPerFrame * desc.mFramesPerPacket;AURenderCallbackStruct cb;cb.inputProcRefCon = (__bridge void *)(self);cb.inputProc = handleInputBuffer;status = AudioUnitSetProperty(self.componetInstance, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 1, &desc, sizeof(desc));status = AudioUnitSetProperty(self.componetInstance, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Global, 1, &cb, sizeof(cb));status = AudioUnitInitialize(self.componetInstance);if (noErr != status) {[self handleAudioComponentCreationFailure];}[session setPreferredSampleRate:_configuration.audioSampleRate error:nil];[session setActive:YES error:nil];

视频的录制：调用GPUImage中的GPUImageVideoCamera

_videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:_configuration.avSessionPreset cameraPosition:AVCaptureDevicePositionFront];
_videoCamera.outputImageOrientation = _configuration.orientation;
_videoCamera.horizontallyMirrorFrontFacingCamera = NO;
_videoCamera.horizontallyMirrorRearFacingCamera = NO;
_videoCamera.frameRate = (int32_t)_configuration.videoFrameRate;_gpuImageView = [[GPUImageView alloc] initWithFrame:[UIScreen mainScreen].bounds];
[_gpuImageView setFillMode:kGPUImageFillModePreserveAspectRatioAndFill];
[_gpuImageView setAutoresizingMask:UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight];[_gpuImageView setInputRotation:kGPUImageFlipHorizonal atIndex:0];

转载请注明原地址，Clang的博客：https://chenhu1001.github.io 谢谢！