视频录制
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。
// 7.0AVAuthorizationStatusauthStatus = [AVCaptureDeviceauthorizationStatusForMediaType: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([UIImagePickerControllerisSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {UIImagePickerController*picker = [[UIImagePickerControlleralloc] 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]; [selfpresentViewController:picker animated:YEScompletion: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
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。
AVAuthorizationStatusauthStatus = [AVCaptureDeviceauthorizationStatusForMediaType: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([UIImagePickerControllerisSourceTypeAvailable:UIImagePickerControllerSourceTypeSavedPhotosAlbum]) {UIImagePickerController*picker = [[UIImagePickerControlleralloc] init]; picker.delegate=self; picker.allowsEditing=YES; picker.sourceType=UIImagePickerControllerSourceTypeSavedPhotosAlbum; picker.mediaTypes= @[(NSString*)kUTTypeMovie]; [selfpresentViewController:picker animated:YEScompletion: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。
保存视频到相册
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"); } } }]; }});
获取视频帧图
同步获取帧图
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 {// resultUIImage*image =nil;// AVAssetImageGeneratorAVAsset*asset = [AVAssetassetWithURL:videoURL];AVAssetImageGenerator*imageGenerator = [[AVAssetImageGeneratoralloc] initWithAsset:asset]; imageGenerator.appliesPreferredTrackTransform=YES;// calculate the midpoint time of videoFloat64 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 systemsCMTime midpoint = CMTimeMakeWithSeconds(duration /2.0,600);// get the image fromNSError*error =nil; CMTime actualTime;// Returns a CFRetained CGImageRef for an asset at or near the specified time.// So we should mannully release itCGImageRefcenterFrameImage = [imageGeneratorcopyCGImageAtTime:midpoint actualTime:&actualTime error:&error];if(centerFrameImage !=NULL) { image = [[UIImagealloc] initWithCGImage:centerFrameImage];// Release the CFRetained imageCGImageRelease(centerFrameImage); }returnimage;}
异步获取帧图
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 {// AVAssetImageGeneratorAVAsset*asset = [AVAssetassetWithURL:videoURL];AVAssetImageGenerator*imageGenerator = [[AVAssetImageGeneratoralloc] initWithAsset:asset]; imageGenerator.appliesPreferredTrackTransform=YES;// calculate the midpoint time of videoFloat64 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 systemsCMTime midpoint = CMTimeMakeWithSeconds(duration /2.0,600);// 异步获取多帧图片NSValue*midTime = [NSValuevalueWithCMTime:midpoint]; [imageGenerator generateCGImagesAsynchronouslyForTimes:@[midTime] completionHandler:^(CMTime requestedTime,CGImageRef_Nullable image, CMTime actualTime,AVAssetImageGeneratorResultresult,NSError* _Nullable error) {if(result ==AVAssetImageGeneratorSucceeded&& image !=NULL) {UIImage*centerFrameImage = [[UIImagealloc] initWithCGImage:image];dispatch_async(dispatch_get_main_queue(), ^{if(completion) { completion(centerFrameImage); } }); }else{dispatch_async(dispatch_get_main_queue(), ^{if(completion) { completion(nil); } }); } }];}
压缩并导出视频
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 URLAVURLAsset*videoAsset = [[AVURLAssetalloc] initWithURL:videoURL options:nil];// Find compatible presets by video asset.NSArray*presets = [AVAssetExportSessionexportPresetsCompatibleWithAsset: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 = [[AVAssetExportSessionalloc] initWithAsset:videoAsset presetName:AVAssetExportPreset640x480];NSString*doc = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];NSString*folder = [doc stringByAppendingPathComponent:@"HYBVideos"];BOOLisDir =NO;BOOLisExist = [[NSFileManagerdefaultManager] fileExistsAtPath:folder isDirectory:&isDir];if(!isExist || (isExist && !isDir)) {NSError*error =nil; [[NSFileManagerdefaultManager] createDirectoryAtPath:folder withIntermediateDirectories:YESattributes:nilerror:&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= [NSURLfileURLWithPath:outPutPath];// Optimize for network use.session.shouldOptimizeForNetworkUse=true;NSArray*supportedTypeArray = session.supportedFileTypes;if([supportedTypeArray containsObject:AVFileTypeMPEG4]) { session.outputFileType=AVFileTypeMPEG4; }elseif(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.outputURLpath]); } }); }else{dispatch_async(dispatch_get_main_queue(), ^{if(completion) { completion(nil); } }); } }]; }}
解决iOS8上录视频引起的偏移bug
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:YEScompletion:^{// for fixing iOS 8.0 problem that frame changed when open camera to record video.self.tabBarController.view.frame= [[UIScreenmainScreen] bounds]; [self.tabBarController.viewlayoutIfNeeded];}];
Tip：记得在选择或者取消的代理中都调用！
文／标哥的技术博客（简书作者）
原文链接：http://www.jianshu.com/p/6f23f608048e
著作权归作者所有，转载请联系作者获得授权，并标注“简书作者”。
