iOS直播技术分享-音视频采集（一）
2016-06-22 本文已影响2555人
Clang的技术博客
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: self
selector: @selector(handleRouteChange:)
name: AVAudioSessionRouteChangeNotification
object: session];
[[NSNotificationCenter defaultCenter] addObserver: self
selector: @selector(handleInterruption:)
name: AVAudioSessionInterruptionNotification
object: 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];
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