使用系统界面拍摄视频及系统问题

目前，将视频捕获集成到你的应用中的最简单的方法是使用 UIImagePickerController。这是一个封装了完整视频捕获管线和相机 UI 的 view controller。用UIImagePickerController可以自定义系统提供的界面来拍摄并保存视频和照片。

UIImagePickerController 里有几个比较重要的属性.

• ** Source type** :
  这个参数是用来确定是调用摄像头还是调用图片库.
  UIImagePickerControllerSourceTypeCamera : 提供调用摄像头的界面来拍摄照片视频。
  UIImagePickerControllerSourceTypePhotoLibrary 调用图片库作为UIImagePickerController数据源。
  UIImagePickerControllerSourceTypeSavedPhotosAlbum iOS设备中的胶卷相机的图片.作为UIImagePickerController数据源

• Mediatypes:
  NSArray数组。拍摄时：这个属性决定UIImagePickerController界面模式是拍照还是录像.查看已保存多媒体数据，可决定展示的是照片还是视频。
  kUTTypeImage 表示静态图片, kUTTypeMovie表示录像.把空数组传给这个属性会报异常。在设置此属性前，需要用availableMediaTypesForSourceType:类方法判断这种多媒体类型是否被支持。

• **Editing controls **:
  用来指定是否可编辑.将allowsEditing 属性设置为YES表示可编辑,NO表示不可编辑.

• delegate
  id <UINavigationControllerDelegate, UIImagePickerControllerDelegate> delegate:
  使用 UIImagePickerController，必须提供遵守UIImagePickerControllerDelegate和UINavigationControllerDelegate协议
  的delegate对象.UIImagePickerControllerDelegate提供了两个方法来在照相完成后，与UIImagePickerController对象界面进行交互。
  imagePickerController:didFinishPickingMediaWithInfo: delegate使用拍摄的照片或者视频的处理逻辑.
  imagePickerControllerDidCancel(_:) 取消picker view。

步骤

1.首先要检查设备是否支持相机录制, 否则设备不支持相机时，会crash 。

   if ([UIImagePickerController
         isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera] == NO) return;
    UIImagePickerController *camera = [[UIImagePickerController alloc] init];
    camera.sourceType = UIImagePickerControllerSourceTypeCamera;

2.检查在 source type中支持的多媒体类型,并设置mediatypes

camera.mediaTypes = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypeCamera];

如果只想让摄像头只能摄像,而不能拍照,那应该设置mediaTypes
cameraUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeMovie , nil];
kUTTypeImage 对应拍照
kUTTypeMovie 对应摄像
这要导入MobileCoreServices.framework,然后再
#import <MobileCoreServices/UTCoreTypes.h>

3.设置delegate，定义拍摄完成后的交互事件处理

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{
    NSString *mediaType = [info objectForKey: UIImagePickerControllerMediaType];
    UIAlertView *alertView =  [[UIAlertView alloc] initWithTitle:@"选择视频" message:nil delegate:self cancelButtonTitle:@"好" otherButtonTitles:nil, nil];
    [alertView show];
    NSLog(@"didFinishPickingMediaWithInfo info=%@;type = %@", info, mediaType);
}

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker
{
    NSLog(@"imagePickerControllerDidCancel");
    
    [picker dismissViewControllerAnimated:YES completion:nil];
}

完整代码：

ViewController.m

#import <MobileCoreServices/UTCoreTypes.h>
#import <MediaPlayer/MediaPlayer.h>
#import <AVFoundation/AVFoundation.h>

#import "ViewController.h"

@interface ViewController () <UINavigationControllerDelegate, UIImagePickerControllerDelegate, UIAlertViewDelegate>

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithTitle:@"拍摄" style:UIBarButtonItemStylePlain target:self action:@selector(startCameraControllerFromViewController:)];
    self.navigationItem.rightBarButtonItem = rightItem;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{
    NSString *mediaType = [info objectForKey: UIImagePickerControllerMediaType];
    UIAlertView *alertView =  [[UIAlertView alloc] initWithTitle:@"选择视频" message:nil delegate:self cancelButtonTitle:@"好" otherButtonTitles:nil, nil];
    [alertView show];
    NSLog(@"didFinishPickingMediaWithInfo info=%@;type = %@", info, mediaType);
}

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker
{
    NSLog(@"imagePickerControllerDidCancel");
    
    [picker dismissViewControllerAnimated:YES completion:nil];
}

// 设备是否被授权访问相机
-(BOOL)isCameraAuthorized
{
    AVAuthorizationStatus auth = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
    return (auth == AVAuthorizationStatusAuthorized);
}

// 请访问求相机授权
- (void)requestCameraAuthorization
{
    NSString *title = @"请在\设置-隐私-相机\"选项中，允许访问你的相机。";
    AVAuthorizationStatus auth = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
    if (auth == AVAuthorizationStatusNotDetermined) {
        [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
            dispatch_async(dispatch_get_main_queue(), ^{
                UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:nil delegate:self cancelButtonTitle:@"好" otherButtonTitles:nil];
                [alertView show];
            });
        }];
    }
    else {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:nil delegate:self cancelButtonTitle:@"好" otherButtonTitles:nil];
        [alertView show];
    }
}

- (void)startCameraControllerFromViewController: (UIViewController*)controller
{
    if (![self isCameraAuthorized]) {
        [self requestCameraAuthorization];
    }
    
    if ([UIImagePickerController
         isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera] == NO) return;
    
    UIImagePickerController *camera = [[UIImagePickerController alloc] init];
    camera.sourceType = UIImagePickerControllerSourceTypeCamera;
    camera.delegate = self;
    
    camera.mediaTypes = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypeCamera];
    
    [self presentViewController:camera animated:YES completion:nil];

}
@end

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    self.viewController = [[ViewController alloc] init];
    self.navigationController = [[UINavigationController alloc] init];
    [self.navigationController pushViewController:self.viewController animated:YES];
    self.window.rootViewController = self.navigationController;
    return YES;
}

bug：

横向拍摄视频，完成拍摄后点击“使用视频”，摄像头被打开，背景出现摄像流。

bug.png

设备和系统：
iPhone6Plus 9.1 ，上述情况
iPhone5s 8.3 , 上述情况
iPhone4s 7.1.1, 上述情况，但是显示是已拍摄视频的最后一帧。

问题原因：
调用系统摄像机录像时,UIImagePickerController视图有两个关键子view，CMKVideoPreviewView和PLAVPlayerView。
PLAVPlayerView 用来播放已录制的视频。
CMKVideoPreviewView 负责展示摄像头实时拍摄的视频流。 PreviewView在不同系统版本有不同的名字：

• 9.1系统的类名是CMKVideoPreviewView;
• 8.3系统是CAMVideoPreviewView;
• 7.1系统是 PLVideoPreviewView）

视图层次结构：CMKVideoPreviewView在下，PLAVPlayerView 在上。横屏拍摄视频，完成拍摄后，由于UIImagePickerController官方只支持竖屏模式，系统自动转为竖屏模式并更新PLVideoPosterFrameView的UIImageView（已录制视频的快照）的frame为 (0, 212,75, 414, 310,5),所以原本被遮挡的CMKVideoPreviewView就显示出来了。

Paste_Image.png

解决方案：
思路：在点击“使用视频”之后，弹出“压缩”toast提示之前，获取CMKVideoPreviewView对象的指针，并讲该对象的hidden属性设为YES.由于CMKVideoPreviewView是private frameworks中的类，无法直接获取对象，但可通过public api : view.subviews ,在子view中递归查找目标对象，安全地获取到该对象。此方法可以通过appstore的审查。 如何安全使用私有库类

- (void)setVideoPreviewHidden:(BOOL)hidden inPicker:(UIImagePickerController *)picker
{
    UIView *view = nil;
    float systemVersion = UIDevice.currentDevice.systemVersion.floatValue;
    if (systemVersion>= 10.0) {
        return;
    }
    else if (systemVersion>= 9.0) {
        view = UIViewFindSubview(picker.view, [NSClassFromString(@"CMKVideoPreviewView") class]);
    }
    else if (systemVersion >= 8.0) {
        view = UIViewFindSubview(picker.view, [NSClassFromString(@"CAMVideoPreviewView") class]);
    }
    else if (systemVersion >= 7.0) {
        view = UIViewFindSubview(picker.view, [NSClassFromString(@"PLVideoPreviewView") class]);
    }
    view.hidden = hidden;
}

NS_INLINE UIView *UIViewFindSubview(UIView *view, Class viewClass)
{
 for (UIView *subview in view.subviews) {
  if ([subview isKindOfClass:viewClass])  {
   return subview;
  } else {
   UIView *ret = UIViewFindSubview(subview, viewClass);
   if (ret) return ret;
  }
 }
 
 return nil;
}

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