首先，我们弹出系统的视频录制界面，也就是UIImagePickerController控制器来实现，但是我们需要验证用户授权，只有有录制视频的权限，才能继续往下。
我们还需要判断UIImagePickerControllerSourceTypeCamera是否支持，比如模拟器就不支持，当然真机是否有不支持的并不知道，不过更安全的写法是要这么写的。视频录制可以设置录制的视频的质量，也就是分辨率的高低，通过videoQuality属性来设置。我们还可以设置录制视频的最大时长，通过videoMaximumDuration属性设置，比如这里设置为5分钟。
// 7.0AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];if (authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied) { NSLog(@"摄像头已被禁用，您可在设置应用程序中进行开启"); return;}if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) { UIImagePickerController *picker = [[UIImagePickerController alloc] init]; picker.delegate = self; picker.allowsEditing = YES; picker.sourceType = UIImagePickerControllerSourceTypeCamera; picker.videoQuality = UIImagePickerControllerQualityType640x480; //录像质量 picker.videoMaximumDuration = 5 * 60.0f; // 限制视频录制最多不超过5分钟 picker.mediaTypes = @[(NSString *)kUTTypeMovie]; [self PResentViewController:picker animated:YES completion:NULL]; self.shouldAsync = YES;} else { NSLog(@"手机不支持摄像");}然后实现代理，就可以拿到录制的视频了。
从相册选择视频与弹出录制视频的代码差不多，只是sourceType不一样而已。我们一样要求先判断权限，用户是否授权，若不允许，就没有办法了。
指定sourceType为UIImagePickerControllerSourceTypeSavedPhotosAlbum就是获取保存到相册中的media。我们还要指定mediaTypes，只需要设置为kUTTypeMovie就可以了。
AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];if (authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied) { NSLog(@"摄像头已被禁用，您可在设置应用程序中进行开启"); return;}if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeSavedPhotosAlbum]) { UIImagePickerController *picker = [[UIImagePickerController alloc] init]; picker.delegate = self; picker.allowsEditing = YES; picker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum; picker.mediaTypes = @[(NSString *)kUTTypeMovie]; [self presentViewController:picker animated:YES completion:NULL]; self.shouldAsync = NO;} else { NSLog(@"手机不支持摄像");}同样，实现代理方法，就可以取到所选择的视频了。
写入相册可以通过ALAssetsLibrary类来实现，它提供了写入相册的API，异步写入，完成是要回到主线程更新UI：
NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL];ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];dispatch_async(dispatch_get_global_queue(0, 0), ^{ // 判断相册是否兼容视频，兼容才能保存到相册 if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:videoURL]) { [library writeVideoAtPathToSavedPhotosAlbum:videoURL completionBlock:^(NSURL *assetURL, NSError *error) { dispatch_async(dispatch_get_main_queue(), ^{ // 写入相册 if (error == nil) { NSLog(@"写入相册成功"); } else { NSLog(@"写入相册失败"); } } }]; }});同步获取中间帧，需要指定哪个时间点的帧，当获取到以后，返回来的图片对象是CFRetained过的，需要外面手动CGImageRelease一下，释放内存。通过AVAsset来访问具体的视频资源，然后通过AVAssetImageGenerator图片生成器来生成某个帧图片：
// Get the video's center frame as video poster image- (UIImage *)frameImageFromVideoURL:(NSURL *)videoURL { // result UIImage *image = nil; // AVAssetImageGenerator AVAsset *asset = [AVAsset assetWithURL:videoURL]; AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset]; imageGenerator.appliesPreferredTrackTransform = YES; // calculate the midpoint time of video Float64 duration = CMTimeGetSeconds([asset duration]); // 取某个帧的时间，参数一表示哪个时间（秒），参数二表示每秒多少帧 // 通常来说，600是一个常用的公共参数，苹果有说明: // 24 frames per second (fps) for film, 30 fps for NTSC (used for TV in North America and // Japan), and 25 fps for PAL (used for TV in Europe). // Using a timescale of 600, you can exactly represent any number of frames in these systems CMTime midpoint = CMTimeMakeWithSeconds(duration / 2.0, 600); // get the image from NSError *error = nil; CMTime actualTime; // Returns a CFRetained CGImageRef for an asset at or near the specified time. // So we should mannully release it CGImageRef centerFrameImage = [imageGenerator copyCGImageAtTime:midpoint actualTime:&actualTime error:&error]; if (centerFrameImage != NULL) { image = [[UIImage alloc] initWithCGImage:centerFrameImage]; // Release the CFRetained image CGImageRelease(centerFrameImage); } return image;}异步获取某个帧的图片，与同步相比，只是调用API不同，可以传多个时间点，然后计算出实际的时间并返回图片，但是返回的图片不需要我们手动再release了。有可能取不到图片，所以还需要判断是否是AVAssetImageGeneratorSucceeded，是才转换图片：
// 异步获取帧图片，可以一次获取多帧图片- (void)centerFrameImageWithVideoURL:(NSURL *)videoURL completion:(void (^)(UIImage *image))completion { // AVAssetImageGenerator AVAsset *asset = [AVAsset assetWithURL:videoURL]; AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset]; imageGenerator.appliesPreferredTrackTransform = YES; // calculate the midpoint time of video Float64 duration = CMTimeGetSeconds([asset duration]); // 取某个帧的时间，参数一表示哪个时间（秒），参数二表示每秒多少帧 // 通常来说，600是一个常用的公共参数，苹果有说明: // 24 frames per second (fps) for film, 30 fps for NTSC (used for TV in North America and // Japan), and 25 fps for PAL (used for TV in Europe). // Using a timescale of 600, you can exactly represent any number of frames in these systems CMTime midpoint = CMTimeMakeWithSeconds(duration / 2.0, 600); // 异步获取多帧图片 NSValue *midTime = [NSValue valueWithCMTime:midpoint]; [imageGenerator generateCGImagesAsynchronouslyForTimes:@[midTime] completionHandler:^(CMTime requestedTime, CGImageRef _Nullable image, CMTime actualTime, AVAssetImageGeneratorResult result, NSError * _Nullable error) { if (result == AVAssetImageGeneratorSucceeded && image != NULL) { UIImage *centerFrameImage = [[UIImage alloc] initWithCGImage:image]; dispatch_async(dispatch_get_main_queue(), ^{ if (completion) { completion(centerFrameImage); } }); } else { dispatch_async(dispatch_get_main_queue(), ^{ if (completion) { completion(nil); } }); } }];}压缩视频是因为视频分辨率过高所生成的视频的大小太大了，对于移动设备来说，内存是不能太大的，如果不支持分片上传到服务器，或者不支持流上传、文件上传，而只能支持表单上传，那么必须要限制大小，压缩视频。
就像我们在使用某平台的视频的上传的时候，到现在还没有支持流上传，也不支持文件上传，只支持表单上传，导致视频大一点就会闪退。流上传是上传成功了，但是人家后台不识别，这一次让某平台坑坏了。直接用file上传，也传过去了，上传进度100%了，但是人家那边还是作为失败处理，无奈！
言归正传，压缩、导出视频，需要通过AVAssetExportsession来实现，我们需要指定一个preset，并判断是否支持这个preset，只有支持才能使用。
我们这里设置的preset为AVAssetExportPreset640x480，属于压缩得比较厉害的了，这需要根据服务器视频上传的支持程度而选择的。然后通过调用异步压缩并导出视频：
- (void)compressVideoWithVideoURL:(NSURL *)videoURL savedName:(NSString *)savedName completion:(void (^)(NSString *savedPath))completion { // accessing video by URL AVURLAsset *videoAsset = [[AVURLAsset alloc] initWithURL:videoURL options:nil]; // Find compatible presets by video asset. NSArray *presets = [AVAssetExportSession exportPresetsCompatibleWithAsset:videoAsset]; // Begin to compress video // Now we just compress to low resolution if it supports // If you need to upload to the server, but server does't support to upload by streaming, // You can compress the resolution to lower. Or you can support more higher resolution. if ([presets containsObject:AVAssetExportPreset640x480]) { AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:videoAsset presetName:AVAssetExportPreset640x480]; NSString *doc = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"]; NSString *folder = [doc stringByAppendingPathComponent:@"HYBVideos"]; BOOL isDir = NO; BOOL isExist = [[NSFileManager defaultManager] fileExistsAtPath:folder isDirectory:&isDir]; if (!isExist || (isExist && !isDir)) { NSError *error = nil; [[NSFileManager defaultManager] createDirectoryAtPath:folder withIntermediateDirectories:YES attributes:nil error:&error]; if (error == nil) { NSLog(@"目录创建成功"); } else { NSLog(@"目录创建失败"); } } NSString *outPutPath = [folder stringByAppendingPathComponent:savedName]; session.outputURL = [NSURL fileURLWithPath:outPutPath]; // Optimize for network use. session.shouldOptimizeForNetworkUse = true; NSArray *supportedTypeArray = session.supportedFileTypes; if ([supportedTypeArray containsObject:AVFileTypeMPEG4]) { session.outputFileType = AVFileTypeMPEG4; } else if (supportedTypeArray.count == 0) { NSLog(@"No supported file types"); return; } else { session.outputFileType = [supportedTypeArray objectAtIndex:0]; } // Begin to export video to the output path asynchronously. [session exportAsynchronouslyWithCompletionHandler:^{ if ([session status] == AVAssetExportSessionStatusCompleted) { dispatch_async(dispatch_get_main_queue(), ^{ if (completion) { completion([session.outputURL path]); } }); } else { dispatch_async(dispatch_get_main_queue(), ^{ if (completion) { completion(nil); } }); } }]; }}在iOS8上有这么一样bug：弹出录制视频页面，再回来发现整个view都往下移动了，可能网上有很多解决办法，下面只是其中一种：
[picker dismissViewControllerAnimated:YES completion:^{ // for fixing iOS 8.0 problem that frame changed when open camera to record video. self.tabBarController.view.frame = [[UIScreen mainScreen] bounds]; [self.tabBarController.view layoutIfNeeded];}];Tip：记得在选择或者取消的代理中都调用！
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