看完熊皮皮的文章后，个人理解的一点小笔记
前记：AVCaptureSession作为一个管理员，管理着input 和output; 由于笔者对视频音频的理解实在是白得不能再白的小白了，因此这里在音视频上不做解释，如果想了解可以查看原文
1, input 对象：AVCaptureDeviceInput 主要与AVCaptureDevice绑定；
AVCaptureDevice 有摄像头和麦克风等；如何获取：
AVCaptureDevice *avCaptureDevice;
//这里MediaType媒体类型，决定获取怎样的硬件源，video为摄像头，audio为
麦克风
NSArray *cameras = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *device in cameras) {
//这里取到后置摄像头
if (device.position == AVCaptureDevicePositionBack) {
avCaptureDevice = device;
}
}
后面再补充如何切换摄像头
2, 创建管理者session，添加input
NSError *error = nil;
AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:avCaptureDevice error:&error];
if (!videoInput)
{
return;
}
AVCaptureSession *avCaptureSession = [[AVCaptureSession alloc] init];
avCaptureSession.sessionPreset = AVCaptureSessionPresetHigh; // sessionPreset为AVCaptureSessionPresetHigh，可不显式指定
[avCaptureSession addInput:videoInput];
3, output对象：AVCaptureVideoDataOutput，需要设置输出相关参数，例如分辨率什么的，还有代理协议用来处理输出数据
AVCaptureVideoDataOutput *avCaptureVideoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
//YUV420一般用于标清视频，YUV422用于高清视频
NSDictionary*settings = @{(__bridge id)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)};
avCaptureVideoDataOutput.videoSettings = settings;
dispatch_queue_t queue = dispatch_queue_create("com.github.michael-lfx.back_camera_io", NULL);
//这里添加代理，在代理中处理数据, 由于这里是在子线程中处理，后面将会涉及到时间戳帧的排序
[avCaptureVideoDataOutput setSampleBufferDelegate:self queue:queue];
[avCaptureSession addOutput:avCaptureVideoDataOutput];
4, 添加预览界面到view上
AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:avCaptureSession];
previewLayer.frame = self.view.bounds;
previewLayer.videoGravity= AVLayerVideoGravityResizeAspectFill;
[self.view.layer addSublayer:previewLayer];
5, 启动会话。
[avCaptureSession startRunning];
直到这里，你就可以看到通过摄像头获取到的图像了
再来说说代理中数据的处理
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
//这里从sampleBuffer拿到未压缩的数据，pixelBuffer; 小白我尝试audiolist，但是一堆的参数，实在是不解，暂且放弃
CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
if (CVPixelBufferIsPlanar(pixelBuffer)) {
NSLog(@"kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange -> planar buffer");
}
CMVideoFormatDescriptionRef desc = NULL;
CMVideoFormatDescriptionCreateForImageBuffer(NULL, pixelBuffer, &desc);
CFDictionaryRef extensions = CMFormatDescriptionGetExtensions(desc);
NSLog(@"extensions = %@", extensions);
}
输出结果
kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange -> planar buffer
extensions = {
CVBytesPerRow = 2904;
CVImageBufferColorPrimaries = "ITU_R_709_2";
CVImageBufferTransferFunction = "ITU_R_709_2";
CVImageBufferYCbCrMatrix = "ITU_R_709_2";
Version = 2;
}
编码
// 获取摄像头输出图像的宽高
size_t width = CVPixelBufferGetWidth(pixelBuffer);
size_t height = CVPixelBufferGetHeight(pixelBuffer);
static VTCompressionSessionRef compressionSession;
OSStatus status = VTCompressionSessionCreate(NULL,
width, height,
kCMVideoCodecType_H264,
NULL,
NULL,
NULL, &compressionOutputCallback, NULL, &compressionSession);
CMTime presentationTimeStamp = CMTimeMake(frameCount, 1000);
VTEncodeInfoFlags flags;
//开始硬编码
VTCompressionSessionEncodeFrame(compressionSession, pixelBuffer, presentationTimeStamp, kCMTimeInvalid, NULL, NULL, &flags);
编码回调函数实现如下：
static void compressionOutputCallback(void * CM_NULLABLE outputCallbackRefCon,
void * CM_NULLABLE sourceFrameRefCon,
OSStatus status,
VTEncodeInfoFlags infoFlags,
CM_NULLABLE CMSampleBufferRef sampleBuffer ) {
//这里的sampleBuffer中的MBlockData不为空
if (status != noErr) {
NSLog(@"%s with status(%d)", __FUNCTION__, status);
return;
}
if (infoFlags == kVTEncodeInfo_FrameDropped) {
NSLog(@"%s with frame dropped.", __FUNCTION__);
return;
}
/* ------ 辅助调试 ------ */
CMFormatDescriptionRef fmtDesc = CMSampleBufferGetFormatDescription(sampleBuffer);
CFDictionaryRef extensions = CMFormatDescriptionGetExtensions(fmtDesc);
NSLog(@"extensions = %@", extensions);
CMItemCount count = CMSampleBufferGetNumSamples(sampleBuffer);
NSLog(@"samples count = %d", count);
/* ====== 辅助调试 ====== */
// 推流或写入文件
}
打印信息如下：
extensions = {
FormatName = "H.264";
SampleDescriptionExtensionAtoms = {
avcC = <014d0028 ffe1000b 274d0028 ab603c01 13f2a001 000428ee 3c30>;
};
}
samples count = 1
sampleBuffer的详细信息如下：
CMSampleBuffer 0x126e9fd80 retainCount: 1 allocator: 0x1a227cb68
invalid = NO
dataReady = YES
makeDataReadyCallback = 0x0
makeDataReadyRefcon = 0x0
formatDescription = {
mediaType:'vide'
mediaSubType:'avc1'
mediaSpecific: {
codecType: 'avc1' dimensions: 1920 x 1080
}
extensions: {{type = immutable dict, count = 2,
entries =>
0 : {contents = "SampleDescriptionExtensionAtoms"} = {type = immutable dict, count = 1,
entries =>
2 : {contents = "avcC"} = {length = 26, capacity = 26, bytes = 0x014d0028ffe1000b274d0028ab603c01 ... a001000428ee3c30}
}
2 : {contents = "FormatName"} = H.264
}
}
}
sbufToTrackReadiness = 0x0
numSamples = 1
sampleTimingArray[1] = {
{PTS = {196709596065916/1000000000 = 196709.596}, DTS = {INVALID}, duration = {INVALID}},
}
sampleSizeArray[1] = {
sampleSize = 5707,
}
sampleAttachmentsArray[1] = {
sample 0:
DependsOnOthers = false
}
dataBuffer = 0x126e9fc50