AVCaptureVideoPreviewLayer

用于显示摄像头采集到的实时视频预览，可以直接添加到视图层次结构中。
AVCaptureVideoPreviewLayer可以嵌入

AVCaptureSession

处理摄像头捕获的数据封装后给屏幕

AVCaptureConnection

用于管理捕获会话中的数据流连接，包括视频、音频和元数据的连接。通过这个连接，你可以设置或查询与视频预览相关的属性，例如视频方向、视频镜像等。

最简单的demo

main.m

//
//  main.m
//  cameraTest
//
//  Created by Renkai Yang on 12/8/23.
//#import <UIKit/UIKit.h>
#import "AppDelegate.h"
#import "ViewController.h"
int main(int argc, char * argv[]) {NSString * appDelegateClassName;@autoreleasepool {// Setup code that might create autoreleased objects goes here.appDelegateClassName = NSStringFromClass([AppDelegate class]);CameraViewController *cameraViewController = [[CameraViewController alloc] init];[cameraViewController viewDidLoad];
//                [[NSRunLoop currentRunLoop] run];}return UIApplicationMain(argc, argv, nil, appDelegateClassName);
}

viewController.m

#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>@interface CameraViewController : UIViewController@property (nonatomic, strong) AVCaptureSession *captureSession;
@property (nonatomic, strong) AVCaptureVideoPreviewLayer *previewLayer;@end@implementation CameraViewController- (void)viewDidLoad {[super viewDidLoad];// 创建 AVCaptureSessionself.captureSession = [[AVCaptureSession alloc] init];// 设置摄像头为后置摄像头AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];if (videoDevice) {NSError *error;AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];if (!error) {[self.captureSession addInput:videoInput];} else {NSLog(@"Error setting up video input: %@", error);}} else {NSLog(@"Video device not available");}// 创建 AVCaptureVideoPreviewLayerself.previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;self.previewLayer.frame = self.view.layer.bounds;[self.view.layer addSublayer:self.previewLayer];//    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
//    for (AVCaptureDevice *device in devices) {
//        NSLog(@"Device name: %@", [device localizedName]);
//        NSLog(@"Device position: %ld", (long)[device position]);
//    }// 启动 AVCaptureSessiondispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{[self.captureSession startRunning];});
}@end

ViewController.h

#import <UIKit/UIKit.h>@interface CameraViewController : UIViewController@end

info.plist