前言
AVFoundation框架是iOS中很重要的框架，所有与音视频相关的软硬件控制都在这个框架里。本文主要介绍iOS媒体捕捉和视频采集。
媒体捕捉流程
媒体捕捉(网侵删).png
简单介绍
- AVCaptureSession：媒体捕获会话（包括音频和视频），负责把捕获的音视频数据输出到输出设备中，一个AVCaptureSession可以有多个输入输出。
在视频或音频捕捉时，客户端可以实例AVCaptureSession，添加适当的AVCaptureInputs、AVCaptureDeviceInput和输出。 - AVCaptureInput和AVCaptureDevice：设备输入数据管理对象，可以根据AVCaptureDevice创建对应AVCaptureDeviceInput对象，该对象将会被添加到AVCaptureSession中管理。
- AVCaptureOutput：设备输出数据管理对象。
- AVCaptureVideoPreviewLayer和AVSampleBufferDisplayLayer，相机拍摄预览图层，是CALayer的子类，前者创建需要AVCaptureSession对象，后者可以直接创建，添加CMSampleBufferRef进行展示。
相关代码展示
- (void)configureCamera{
/// 参数设置
// 默认后置摄像头
AVCaptureDevicePosition position = AVCaptureDevicePositionBack;
// 帧率
int frameRate = 25;
// 显色方案
OSType videoFormat = kCVPixelFormatType_32BGRA;
// 分辨率高
int resolutionHeight = 720;
/// 创建AVCaptureSession对象
AVCaptureSession *session = [[AVCaptureSession alloc] init];
/// 设置分辨率
session.sessionPreset = AVCaptureSessionPreset1280x720;
/// 获取摄像头
AVCaptureDevice *captureDevice;
// 默认AVCaptureDevicePositionBack，后置摄像头
AVCaptureDeviceDiscoverySession *deviceDiscoverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:position];
NSArray *devices = deviceDiscoverySession.devices;
for (AVCaptureDevice *device in devices) {
if (AVCaptureDevicePositionBack == device.position) {
captureDevice = device;
}else if (AVCaptureDevicePositionFront == device.position){
captureDevice = device;
}
}
/// 设置帧率和分辨率高度
BOOL isSuccess = NO;
for(AVCaptureDeviceFormat *vFormat in [captureDevice formats]) {
CMFormatDescriptionRef description = vFormat.formatDescription;
float maxRate = ((AVFrameRateRange*) [vFormat.videoSupportedFrameRateRanges objectAtIndex:0]).maxFrameRate;
if (maxRate >= frameRate && CMFormatDescriptionGetMediaSubType(description) == videoFormat) {
if ([captureDevice lockForConfiguration:NULL] == YES) {
// 对比镜头支持的分辨率和当前设置的分辨率
CMVideoDimensions dims = CMVideoFormatDescriptionGetDimensions(description);
if (dims.height == resolutionHeight && dims.width == [self.class getResolutionWidthByHeight:resolutionHeight]) {
[session beginConfiguration];
if ([captureDevice lockForConfiguration:NULL]){
captureDevice.activeFormat = vFormat;
[captureDevice setActiveVideoMinFrameDuration:CMTimeMake(1, frameRate)];
[captureDevice setActiveVideoMaxFrameDuration:CMTimeMake(1, frameRate)];
[captureDevice unlockForConfiguration];
}
[session commitConfiguration];
isSuccess = YES;
}
}else {
NSLog(@"%s: 失败",__func__);
}
}
}
NSError *error;
//添加输入
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
if (error != noErr) {
NSLog(@"配置设备输入失败:%@",error.localizedDescription);
return;
}
[session addInput:input];
//添加输出
AVCaptureVideoDataOutput *videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
if ([session canAddOutput:videoDataOutput]) {
[session addOutput:videoDataOutput];
}
videoDataOutput.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:videoFormat]
forKey:(id)kCVPixelBufferPixelFormatTypeKey];
//当此属性的值为YES时，接收方将立即丢弃捕获的帧，而处理现有帧的调度队列在captureOutput:didOutputSampleBuffer:fromConnection: delegate方法中被阻塞。当此属性的值为NO时，将允许委托在丢弃新帧之前有更多的时间处理旧帧，但应用程序的内存使用量可能会显著增加。默认值为“YES”。（机翻）
videoDataOutput.alwaysDiscardsLateVideoFrames = NO;
//创建一个队列接收数据
dispatch_queue_t videoQueue = dispatch_queue_create("video_receive_queue", NULL);
[videoDataOutput setSampleBufferDelegate:self queue:videoQueue];
//创建接收对象
AVCaptureVideoPreviewLayer *videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
videoPreviewLayer.backgroundColor = [[UIColor blackColor] CGColor];
CGRect frame = [videoPreviewLayer bounds];
NSLog(@"previewViewLayer = %@",NSStringFromCGRect(frame));
//设置尺寸和填充方式
[videoPreviewLayer setFrame:[UIScreen mainScreen].bounds];
[videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
if ([[videoPreviewLayer connection] isVideoOrientationSupported]) {
[videoPreviewLayer.connection setVideoOrientation:AVCaptureVideoOrientationPortrait];
}else{
NSLog(@"不支持视频定向");
}
//需要在哪个view上展示
UIView *showView = [[UIView alloc] init];
[showView.layer insertSublayer:videoPreviewLayer atIndex:0];
}
//采集视频的回调，如果需要编码H264/H265,在这里操作
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
/*
//另一种展示方式
AVSampleBufferDisplayLayer *previewLayer = [AVSampleBufferDisplayLayer layer];
previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[previewLayer enqueueSampleBuffer:sampleBuffer];
//需要在哪个view上展示
UIView *showView = [[UIView alloc] init];
[showView.layer insertSublayer:previewLayer atIndex:0];
*/
}
///需要考虑横竖屏情况，这里暂未考虑
+ (int)getResolutionWidthByHeight:(int)height {
switch (height) {
case 2160:
return 3840;
case 1080:
return 1920;
case 720:
return 1280;
case 480:
return 640;
default:
return -1;
}
}
Tips：配置采集之前，记得申请摄像头权限，如果没有权限，需要自己做判断，这里省略。
Demo地址整理后奉上。
有其他不明白的，可以留言，看到就会回复。
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