自定义相机
2020-11-12 本文已影响0人
凯歌948
AVFoundation
Assets：
加载、检查和导出媒体资产和元数据，并执行媒体示例数据的低级读写。
Playback
获取并检查媒体资产;用于回放和自定义回放行为的队列媒体;编辑和合并资产;导入和导出原始媒体流。
Capture
拍摄照片，录制视频和音频;配置内置摄像头和麦克风或外部捕获设备。
Editing
在一个组合中合并、编辑和混合来自多个来源的音频和视频轨道。
Audio
播放、记录和处理音频;配置你的应用程序的系统音频行为。
Speech
转换文本到语音
捕捉会话：AVCaptureSession
捕捉设备：AVCaptureDevice
捕捉设备输入：AVCaptureDeviceInput
捕捉设备输出：AVCaptureOutput
静态图片输出：AVCaptureStillImageOutput
电影文件输出：AVCaputureMovieFileOutput
音频数据输出：AVCaputureAudioDataOutput
视频数据输出：AVCaputureVideoDataOutput
捕捉设备连接：AVCaptureConnection
捕捉设备预览：AVCaptureVideoPreviewLayer
** 此demo包含的功能有：视频录制，拍照，生成缩略图，切换摄像头，摄像头聚焦、曝光、重设聚焦或曝光，手电筒，闪光灯 **
AVFoundation自定义相机demo
头文件
#import <AVFoundation/AVFoundation.h>
extern NSString *const THThumbnailCreatedNotification;
@protocol THCameraControllerDelegate <NSObject>
// 1发生错误事件是，需要在对象委托上调用一些方法来处理
- (void)deviceConfigurationFailedWithError:(NSError *)error;
- (void)mediaCaptureFailedWithError:(NSError *)error;
- (void)assetLibraryWriteFailedWithError:(NSError *)error;
@end
@interface THCameraController : NSObject
@property (weak, nonatomic) id<THCameraControllerDelegate> delegate;
@property (nonatomic, strong, readonly) AVCaptureSession *captureSession;
// 2 用于设置、配置视频捕捉会话
- (BOOL)setupSession:(NSError **)error;
- (void)startSession;
- (void)stopSession;
// 3 切换不同的摄像头
- (BOOL)switchCameras;
- (BOOL)canSwitchCameras;
@property (nonatomic, readonly) NSUInteger cameraCount;
@property (nonatomic, readonly) BOOL cameraHasTorch; //手电筒
@property (nonatomic, readonly) BOOL cameraHasFlash; //闪光灯
@property (nonatomic, readonly) BOOL cameraSupportsTapToFocus; //聚焦
@property (nonatomic, readonly) BOOL cameraSupportsTapToExpose;//曝光
@property (nonatomic) AVCaptureTorchMode torchMode; //手电筒模式
@property (nonatomic) AVCaptureFlashMode flashMode; //闪光灯模式
// 4 聚焦、曝光、重设聚焦、曝光的方法
- (void)focusAtPoint:(CGPoint)point;
- (void)exposeAtPoint:(CGPoint)point;
- (void)resetFocusAndExposureModes;
// 5 实现捕捉静态图片 & 视频的功能
//捕捉静态图片
- (void)captureStillImage;
//视频录制
//开始录制
- (void)startRecording;
//停止录制
- (void)stopRecording;
//获取录制状态
- (BOOL)isRecording;
//录制时间
- (CMTime)recordedDuration;
@end
实现文件
#import "THCameraController.h"
#import <AVFoundation/AVFoundation.h>
#import <AssetsLibrary/AssetsLibrary.h>
#import "NSFileManager+THAdditions.h"
NSString *const THThumbnailCreatedNotification = @"THThumbnailCreated";
static const NSString *THCameraAdjustingExposureContext;
@interface THCameraController () <AVCaptureFileOutputRecordingDelegate>
@property (strong, nonatomic) dispatch_queue_t videoQueue; //视频队列
@property (strong, nonatomic) AVCaptureSession *captureSession;// 捕捉会话
@property (weak, nonatomic) AVCaptureDeviceInput *activeVideoInput;//输入
@property (strong, nonatomic) AVCaptureStillImageOutput *imageOutput;//输出图片
@property (strong, nonatomic) AVCaptureMovieFileOutput *movieOutput;//输出小视频
@property (strong, nonatomic) NSURL *outputURL;
@end
@implementation THCameraController
- (BOOL)setupSession:(NSError **)error {
//创建捕捉会话。AVCaptureSession 是捕捉场景的中心枢纽
self.captureSession = [[AVCaptureSession alloc]init];
/*
AVCaptureSessionPresetHigh
AVCaptureSessionPresetMedium
AVCaptureSessionPresetLow
AVCaptureSessionPreset640x480
AVCaptureSessionPreset1280x720
AVCaptureSessionPresetPhoto
*/
//设置图像的分辨率
self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;
//拿到默认视频捕捉设备 iOS系统返回后置摄像头
AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
//将捕捉设备封装成AVCaptureDeviceInput
//注意：为会话添加捕捉设备，必须将设备封装成AVCaptureDeviceInput对象
AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:error];
//判断videoInput是否有效
if (videoInput)
{
//canAddInput：测试是否能被添加到会话中
if ([self.captureSession canAddInput:videoInput])
{
//将videoInput 添加到 captureSession中
[self.captureSession addInput:videoInput];
self.activeVideoInput = videoInput;
}
}else
{
return NO;
}
//选择默认音频捕捉设备 即返回一个内置麦克风
AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
//为这个设备创建一个捕捉设备输入
AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:error];
//判断audioInput是否有效
if (audioInput) {
//canAddInput：测试是否能被添加到会话中
if ([self.captureSession canAddInput:audioInput])
{
//将audioInput 添加到 captureSession中
[self.captureSession addInput:audioInput];
}
}else
{
return NO;
}
//AVCaptureStillImageOutput 实例 从摄像头捕捉静态图片
self.imageOutput = [[AVCaptureStillImageOutput alloc]init];
//配置字典：希望捕捉到JPEG格式的图片
self.imageOutput.outputSettings = @{AVVideoCodecKey:AVVideoCodecJPEG};
//输出连接 判断是否可用，可用则添加到输出连接中去
if ([self.captureSession canAddOutput:self.imageOutput])
{
[self.captureSession addOutput:self.imageOutput];
}
//创建一个AVCaptureMovieFileOutput 实例，用于将Quick Time 电影录制到文件系统
self.movieOutput = [[AVCaptureMovieFileOutput alloc]init];
//输出连接 判断是否可用，可用则添加到输出连接中去
if ([self.captureSession canAddOutput:self.movieOutput])
{
[self.captureSession addOutput:self.movieOutput];
}
//视频串行队列
self.videoQueue = dispatch_queue_create("cc.VideoQueue", NULL);
return YES;
}
- (void)startSession {
//检查是否处于运行状态
if (![self.captureSession isRunning])
{
//使用同步调用会损耗一定的时间，则用异步的方式处理
dispatch_async(self.videoQueue, ^{
[self.captureSession startRunning];
});
}
}
- (void)stopSession {
//检查是否处于运行状态
if ([self.captureSession isRunning])
{
//使用异步方式，停止运行
dispatch_async(self.videoQueue, ^{
[self.captureSession stopRunning];
});
}
}
#pragma mark - Device Configuration 配置摄像头支持的方法
- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position {
//获取可用视频设备
NSArray *devicess = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
//遍历可用的视频设备 并返回position 参数值
for (AVCaptureDevice *device in devicess)
{
if (device.position == position) {
return device;
}
}
return nil;
}
- (AVCaptureDevice *)activeCamera {
//返回当前捕捉会话对应的摄像头的device 属性
return self.activeVideoInput.device;
}
//返回当前未激活的摄像头
- (AVCaptureDevice *)inactiveCamera {
//通过查找当前激活摄像头的反向摄像头获得，如果设备只有1个摄像头，则返回nil
AVCaptureDevice *device = nil;
if (self.cameraCount > 1)
{
if ([self activeCamera].position == AVCaptureDevicePositionBack) {
device = [self cameraWithPosition:AVCaptureDevicePositionFront];
}else
{
device = [self cameraWithPosition:AVCaptureDevicePositionBack];
}
}
return device;
}
//判断是否有超过1个摄像头可用
- (BOOL)canSwitchCameras {
return self.cameraCount > 1;
}
//可用视频捕捉设备的数量
- (NSUInteger)cameraCount {
return [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count];
}
//切换摄像头
- (BOOL)switchCameras {
//判断是否有多个摄像头
if (![self canSwitchCameras])
{
return NO;
}
//获取当前设备的反向设备
NSError *error;
AVCaptureDevice *videoDevice = [self inactiveCamera];
//将输入设备封装成AVCaptureDeviceInput
AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
//判断videoInput 是否为nil
if (videoInput)
{
//标注原配置变化开始
[self.captureSession beginConfiguration];
//将捕捉会话中，原本的捕捉输入设备移除
[self.captureSession removeInput:self.activeVideoInput];
//判断新的设备是否能加入
if ([self.captureSession canAddInput:videoInput])
{
//能加入成功，则将videoInput 作为新的视频捕捉设备
[self.captureSession addInput:videoInput];
//将获得设备 改为 videoInput
self.activeVideoInput = videoInput;
}else
{
//如果新设备，无法加入。则将原本的视频捕捉设备重新加入到捕捉会话中
[self.captureSession addInput:self.activeVideoInput];
}
//配置完成后， AVCaptureSession commitConfiguration 会分批的将所有变更整合在一起。
[self.captureSession commitConfiguration];
}else
{
//创建AVCaptureDeviceInput 出现错误，则通知委托来处理该错误
[self.delegate deviceConfigurationFailedWithError:error];
return NO;
}
return YES;
}
/*
AVCaptureDevice 定义了很多方法，让开发者控制ios设备上的摄像头。可以独立调整和锁定摄像头的焦距、曝光、白平衡。对焦和曝光可以基于特定的兴趣点进行设置，使其在应用中实现点击对焦、点击曝光的功能。
还可以让你控制设备的LED作为拍照的闪光灯或手电筒的使用
每当修改摄像头设备时，一定要先测试修改动作是否能被设备支持。并不是所有的摄像头都支持所有功能，例如牵制摄像头就不支持对焦操作，因为它和目标距离一般在一臂之长的距离。但大部分后置摄像头是可以支持全尺寸对焦。尝试应用一个不被支持的动作，会导致异常崩溃。所以修改摄像头设备前，需要判断是否支持
*/
#pragma mark - Focus Methods 点击聚焦方法的实现
- (BOOL)cameraSupportsTapToFocus {
//询问激活中的摄像头是否支持兴趣点对焦
return [[self activeCamera]isFocusPointOfInterestSupported];
}
- (void)focusAtPoint:(CGPoint)point {
AVCaptureDevice *device = [self activeCamera];
//是否支持兴趣点对焦 & 是否自动对焦模式
if (device.isFocusPointOfInterestSupported && [device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) {
NSError *error;
//锁定设备准备配置，如果获得了锁
if ([device lockForConfiguration:&error]) {
//将focusPointOfInterest属性设置CGPoint
device.focusPointOfInterest = point;
//focusMode 设置为AVCaptureFocusModeAutoFocus
device.focusMode = AVCaptureFocusModeAutoFocus;
//释放该锁定
[device unlockForConfiguration];
}else{
//错误时，则返回给错误处理代理
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
#pragma mark - Exposure Methods 点击曝光的方法实现
- (BOOL)cameraSupportsTapToExpose {
//询问设备是否支持对一个兴趣点进行曝光
return [[self activeCamera] isExposurePointOfInterestSupported];
}
- (void)exposeAtPoint:(CGPoint)point {
AVCaptureDevice *device = [self activeCamera];
AVCaptureExposureMode exposureMode =AVCaptureExposureModeContinuousAutoExposure;
//判断是否支持 AVCaptureExposureModeContinuousAutoExposure 模式
if (device.isExposurePointOfInterestSupported && [device isExposureModeSupported:exposureMode]) {
[device isExposureModeSupported:exposureMode];
NSError *error;
//锁定设备准备配置
if ([device lockForConfiguration:&error])
{
//配置期望值
device.exposurePointOfInterest = point;
device.exposureMode = exposureMode;
//判断设备是否支持锁定曝光的模式。
if ([device isExposureModeSupported:AVCaptureExposureModeLocked]) {
//支持，则使用kvo确定设备的adjustingExposure属性的状态。
[device addObserver:self forKeyPath:@"adjustingExposure" options:NSKeyValueObservingOptionNew context:&THCameraAdjustingExposureContext];
}
//释放该锁定
[device unlockForConfiguration];
}else
{
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context {
//判断context（上下文）是否为THCameraAdjustingExposureContext
if (context == &THCameraAdjustingExposureContext) {
//获取device
AVCaptureDevice *device = (AVCaptureDevice *)object;
//判断设备是否不再调整曝光等级，确认设备的exposureMode是否可以设置为AVCaptureExposureModeLocked
if(!device.isAdjustingExposure && [device isExposureModeSupported:AVCaptureExposureModeLocked])
{
//移除作为adjustingExposure的self，就不会得到后续变更的通知
[object removeObserver:self forKeyPath:@"adjustingExposure" context:&THCameraAdjustingExposureContext];
//异步方式调回主队列，
dispatch_async(dispatch_get_main_queue(), ^{
NSError *error;
if ([device lockForConfiguration:&error]) {
//修改exposureMode
device.exposureMode = AVCaptureExposureModeLocked;
//释放该锁定
[device unlockForConfiguration];
}else
{
[self.delegate deviceConfigurationFailedWithError:error];
}
});
}
}else
{
[super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}
}
//重新设置对焦&曝光
- (void)resetFocusAndExposureModes {
AVCaptureDevice *device = [self activeCamera];
AVCaptureFocusMode focusMode = AVCaptureFocusModeContinuousAutoFocus;
//获取对焦兴趣点 和 连续自动对焦模式 是否被支持
BOOL canResetFocus = [device isFocusPointOfInterestSupported]&& [device isFocusModeSupported:focusMode];
AVCaptureExposureMode exposureMode = AVCaptureExposureModeContinuousAutoExposure;
//确认曝光度可以被重设
BOOL canResetExposure = [device isFocusPointOfInterestSupported] && [device isExposureModeSupported:exposureMode];
//回顾一下，捕捉设备空间左上角（0，0），右下角（1，1） 中心点则（0.5，0.5）
CGPoint centPoint = CGPointMake(0.5f, 0.5f);
NSError *error;
//锁定设备，准备配置
if ([device lockForConfiguration:&error]) {
//焦点可设，则修改
if (canResetFocus) {
device.focusMode = focusMode;
device.focusPointOfInterest = centPoint;
}
//曝光度可设，则设置为期望的曝光模式
if (canResetExposure) {
device.exposureMode = exposureMode;
device.exposurePointOfInterest = centPoint;
}
//释放锁定
[device unlockForConfiguration];
}else
{
[self.delegate deviceConfigurationFailedWithError:error];
}
}
#pragma mark - Flash and Torch Modes 闪光灯 & 手电筒
//判断是否有闪光灯
- (BOOL)cameraHasFlash {
return [[self activeCamera]hasFlash];
}
//闪光灯模式
- (AVCaptureFlashMode)flashMode {
return [[self activeCamera]flashMode];
}
//设置闪光灯
- (void)setFlashMode:(AVCaptureFlashMode)flashMode {
//获取会话
AVCaptureDevice *device = [self activeCamera];
//判断是否支持闪光灯模式
if ([device isFlashModeSupported:flashMode]) {
//如果支持，则锁定设备
NSError *error;
if ([device lockForConfiguration:&error]) {
//修改闪光灯模式
device.flashMode = flashMode;
//修改完成，解锁释放设备
[device unlockForConfiguration];
}else
{
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
//是否支持手电筒
- (BOOL)cameraHasTorch {
return [[self activeCamera]hasTorch];
}
//手电筒模式
- (AVCaptureTorchMode)torchMode {
return [[self activeCamera]torchMode];
}
//设置是否打开手电筒
- (void)setTorchMode:(AVCaptureTorchMode)torchMode {
AVCaptureDevice *device = [self activeCamera];
if ([device isTorchModeSupported:torchMode]) {
NSError *error;
if ([device lockForConfiguration:&error]) {
device.torchMode = torchMode;
[device unlockForConfiguration];
}else
{
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
#pragma mark - Image Capture Methods 拍摄静态图片
/*
AVCaptureStillImageOutput 是AVCaptureOutput的子类。用于捕捉图片
*/
- (void)captureStillImage {
//获取连接
AVCaptureConnection *connection = [self.imageOutput connectionWithMediaType:AVMediaTypeVideo];
//程序只支持纵向，但是如果用户横向拍照时，需要调整结果照片的方向
//判断是否支持设置视频方向
if (connection.isVideoOrientationSupported) {
//获取方向值
connection.videoOrientation = [self currentVideoOrientation];
}
//定义一个handler 块，会返回1个图片的NSData数据
id handler = ^(CMSampleBufferRef sampleBuffer,NSError *error)
{
if (sampleBuffer != NULL) {
NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:sampleBuffer];
UIImage *image = [[UIImage alloc]initWithData:imageData];
//重点：捕捉图片成功后，将图片传递出去
[self writeImageToAssetsLibrary:image];
}else
{
NSLog(@"NULL sampleBuffer:%@",[error localizedDescription]);
}
};
//捕捉静态图片
[self.imageOutput captureStillImageAsynchronouslyFromConnection:connection completionHandler:handler];
}
//获取方向值
- (AVCaptureVideoOrientation)currentVideoOrientation {
AVCaptureVideoOrientation orientation;
//获取UIDevice 的 orientation
switch ([UIDevice currentDevice].orientation) {
case UIDeviceOrientationPortrait:
orientation = AVCaptureVideoOrientationPortrait;
break;
case UIDeviceOrientationLandscapeRight:
orientation = AVCaptureVideoOrientationLandscapeLeft;
break;
case UIDeviceOrientationPortraitUpsideDown:
orientation = AVCaptureVideoOrientationPortraitUpsideDown;
break;
default:
orientation = AVCaptureVideoOrientationLandscapeRight;
break;
}
return orientation;
return 0;
}
/*
Assets Library 框架
用来让开发者通过代码方式访问iOS photo
注意：会访问到相册，需要修改plist 权限。否则会导致项目崩溃
*/
- (void)writeImageToAssetsLibrary:(UIImage *)image {
//创建ALAssetsLibrary 实例
ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
//参数1:图片（参数为CGImageRef 所以image.CGImage）
//参数2:方向参数 转为NSUInteger
//参数3:写入成功、失败处理
[library writeImageToSavedPhotosAlbum:image.CGImage
orientation:(NSUInteger)image.imageOrientation
completionBlock:^(NSURL *assetURL, NSError *error) {
//成功后，发送捕捉图片通知。用于绘制程序的左下角的缩略图
if (!error)
{
[self postThumbnailNotifification:image];
}else
{
//失败打印错误信息
id message = [error localizedDescription];
NSLog(@"%@",message);
}
}];
}
//发送缩略图通知
- (void)postThumbnailNotifification:(UIImage *)image {
//回到主队列
dispatch_async(dispatch_get_main_queue(), ^{
//发送请求
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc postNotificationName:THThumbnailCreatedNotification object:image];
});
}
#pragma mark - Video Capture Methods 捕捉视频
//判断是否录制状态
- (BOOL)isRecording {
return self.movieOutput.isRecording;
}
//开始录制
- (void)startRecording {
if (![self isRecording]) {
//获取当前视频捕捉连接信息，用于捕捉视频数据配置一些核心属性
AVCaptureConnection * videoConnection = [self.movieOutput connectionWithMediaType:AVMediaTypeVideo];
//判断是否支持设置videoOrientation 属性。
if([videoConnection isVideoOrientationSupported])
{
//支持则修改当前视频的方向
videoConnection.videoOrientation = [self currentVideoOrientation];
}
//判断是否支持视频稳定 可以显著提高视频的质量。只会在录制视频文件涉及
if([videoConnection isVideoStabilizationSupported])
{
videoConnection.enablesVideoStabilizationWhenAvailable = YES;
}
AVCaptureDevice *device = [self activeCamera];
//摄像头可以进行平滑对焦模式操作。即减慢摄像头镜头对焦速度。当用户移动拍摄时摄像头会尝试快速自动对焦。
if (device.isSmoothAutoFocusEnabled) {
NSError *error;
if ([device lockForConfiguration:&error]) {
device.smoothAutoFocusEnabled = YES;
[device unlockForConfiguration];
}else
{
[self.delegate deviceConfigurationFailedWithError:error];
}
}
//查找写入捕捉视频的唯一文件系统URL.
self.outputURL = [self uniqueURL];
//在捕捉输出上调用方法 参数1:录制保存路径 参数2:代理
[self.movieOutput startRecordingToOutputFileURL:self.outputURL recordingDelegate:self];
}
}
- (CMTime)recordedDuration {
return self.movieOutput.recordedDuration;
}
//写入视频唯一文件系统URL
- (NSURL *)uniqueURL {
NSFileManager *fileManager = [NSFileManager defaultManager];
//temporaryDirectoryWithTemplateString 可以将文件写入的目的创建一个唯一命名的目录；
NSString *dirPath = [fileManager temporaryDirectoryWithTemplateString:@"kamera.XXXXXX"];
if (dirPath) {
NSString *filePath = [dirPath stringByAppendingPathComponent:@"kamera_movie.mov"];
return [NSURL fileURLWithPath:filePath];
}
return nil;
}
//停止录制
- (void)stopRecording {
//是否正在录制
if ([self isRecording]) {
[self.movieOutput stopRecording];
}
}
#pragma mark - AVCaptureFileOutputRecordingDelegate
- (void)captureOutput:(AVCaptureFileOutput *)captureOutput
didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL
fromConnections:(NSArray *)connections
error:(NSError *)error {
//错误
if (error) {
[self.delegate mediaCaptureFailedWithError:error];
}else
{
//写入
[self writeVideoToAssetsLibrary:[self.outputURL copy]];
}
self.outputURL = nil;
}
//写入捕捉到的视频
- (void)writeVideoToAssetsLibrary:(NSURL *)videoURL {
//ALAssetsLibrary 实例 提供写入视频的接口
ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
//写资源库写入前，检查视频是否可被写入 （写入前尽量养成判断的习惯）
if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:videoURL]) {
//创建block块
ALAssetsLibraryWriteVideoCompletionBlock completionBlock;
completionBlock = ^(NSURL *assetURL,NSError *error)
{
if (error) {
[self.delegate assetLibraryWriteFailedWithError:error];
}else
{
//用于界面展示视频缩略图
[self generateThumbnailForVideoAtURL:videoURL];
}
};
//执行实际写入资源库的动作
[library writeVideoAtPathToSavedPhotosAlbum:videoURL completionBlock:completionBlock];
}
}
//获取视频左下角缩略图
- (void)generateThumbnailForVideoAtURL:(NSURL *)videoURL {
//在videoQueue 上，
dispatch_async(self.videoQueue, ^{
//建立新的AVAsset & AVAssetImageGenerator
AVAsset *asset = [AVAsset assetWithURL:videoURL];
AVAssetImageGenerator *imageGenerator = [AVAssetImageGenerator assetImageGeneratorWithAsset:asset];
//设置maximumSize 宽为100，高为0 根据视频的宽高比来计算图片的高度
imageGenerator.maximumSize = CGSizeMake(100.0f, 0.0f);
//捕捉视频缩略图会考虑视频的变化（如视频的方向变化），如果不设置，缩略图的方向可能出错
imageGenerator.appliesPreferredTrackTransform = YES;
//获取CGImageRef图片 注意需要自己管理它的创建和释放
CGImageRef imageRef = [imageGenerator copyCGImageAtTime:kCMTimeZero actualTime:NULL error:nil];
//将图片转化为UIImage
UIImage *image = [UIImage imageWithCGImage:imageRef];
//释放CGImageRef imageRef 防止内存泄漏
CGImageRelease(imageRef);
//回到主线程
dispatch_async(dispatch_get_main_queue(), ^{
//发送通知，传递最新的image
[self postThumbnailNotifification:image];
});
});
}
@end
