首先，我們彈出系統(tǒng)的視頻錄制界面，也就是UIImagePickerController控制器來實(shí)現(xiàn)，但是我們需要驗(yàn)證用戶授權(quán)，只有有錄制視頻的權(quán)限，才能繼續(xù)往下。
我們還需要判斷UIImagePickerControllerSourceTypeCamera是否支持，比如模擬器就不支持，當(dāng)然真機(jī)是否有不支持的并不知道，不過更安全的寫法是要這么寫的。視頻錄制可以設(shè)置錄制的視頻的質(zhì)量，也就是分辨率的高低，通過videoQuality屬性來設(shè)置。我們還可以設(shè)置錄制視頻的最大時(shí)長，通過videoMaximumDuration屬性設(shè)置，比如這里設(shè)置為5分鐘。
// 7.0AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];if (authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied) { NSLog(@"攝像頭已被禁用，您可在設(shè)置應(yīng)用程序中進(jìn)行開啟"); return;}if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) { UIImagePickerController *picker = [[UIImagePickerController alloc] init]; picker.delegate = self; picker.allowsEditing = YES; picker.sourceType = UIImagePickerControllerSourceTypeCamera; picker.videoQuality = UIImagePickerControllerQualityType640x480; //錄像質(zhì)量 picker.videoMaximumDuration = 5 * 60.0f; // 限制視頻錄制最多不超過5分鐘 picker.mediaTypes = @[(NSString *)kUTTypeMovie]; [self PResentViewController:picker animated:YES completion:NULL]; self.shouldAsync = YES;} else { NSLog(@"手機(jī)不支持?jǐn)z像");}然后實(shí)現(xiàn)代理，就可以拿到錄制的視頻了。
從相冊選擇視頻與彈出錄制視頻的代碼差不多，只是sourceType不一樣而已。我們一樣要求先判斷權(quán)限，用戶是否授權(quán)，若不允許，就沒有辦法了。
指定sourceType為UIImagePickerControllerSourceTypeSavedPhotosAlbum就是獲取保存到相冊中的media。我們還要指定mediaTypes，只需要設(shè)置為kUTTypeMovie就可以了。
AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];if (authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied) { NSLog(@"攝像頭已被禁用，您可在設(shè)置應(yīng)用程序中進(jìn)行開啟"); 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(@"手機(jī)不支持?jǐn)z像");}同樣，實(shí)現(xiàn)代理方法，就可以取到所選擇的視頻了。
寫入相冊可以通過ALAssetsLibrary類來實(shí)現(xiàn)，它提供了寫入相冊的API，異步寫入，完成是要回到主線程更新UI：
NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL];ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];dispatch_async(dispatch_get_global_queue(0, 0), ^{ // 判斷相冊是否兼容視頻，兼容才能保存到相冊 if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:videoURL]) { [library writeVideoAtPathToSavedPhotosAlbum:videoURL completionBlock:^(NSURL *assetURL, NSError *error) { dispatch_async(dispatch_get_main_queue(), ^{ // 寫入相冊 if (error == nil) { NSLog(@"寫入相冊成功"); } else { NSLog(@"寫入相冊失敗"); } } }]; }});同步獲取中間幀，需要指定哪個(gè)時(shí)間點(diǎn)的幀，當(dāng)獲取到以后，返回來的圖片對象是CFRetained過的，需要外面手動CGImageRelease一下，釋放內(nèi)存。通過AVAsset來訪問具體的視頻資源，然后通過AVAssetImageGenerator圖片生成器來生成某個(gè)幀圖片：
// 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]); // 取某個(gè)幀的時(shí)間，參數(shù)一表示哪個(gè)時(shí)間（秒），參數(shù)二表示每秒多少幀 // 通常來說，600是一個(gè)常用的公共參數(shù)，蘋果有說明: // 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;}異步獲取某個(gè)幀的圖片，與同步相比，只是調(diào)用API不同，可以傳多個(gè)時(shí)間點(diǎn)，然后計(jì)算出實(shí)際的時(shí)間并返回圖片，但是返回的圖片不需要我們手動再release了。有可能取不到圖片，所以還需要判斷是否是AVAssetImageGeneratorSucceeded，是才轉(zhuǎn)換圖片：
// 異步獲取幀圖片，可以一次獲取多幀圖片- (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]); // 取某個(gè)幀的時(shí)間，參數(shù)一表示哪個(gè)時(shí)間（秒），參數(shù)二表示每秒多少幀 // 通常來說，600是一個(gè)常用的公共參數(shù)，蘋果有說明: // 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); // 異步獲取多幀圖片 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); } }); } }];}壓縮視頻是因?yàn)橐曨l分辨率過高所生成的視頻的大小太大了，對于移動設(shè)備來說，內(nèi)存是不能太大的，如果不支持分片上傳到服務(wù)器，或者不支持流上傳、文件上傳，而只能支持表單上傳，那么必須要限制大小，壓縮視頻。
就像我們在使用某平臺的視頻的上傳的時(shí)候，到現(xiàn)在還沒有支持流上傳，也不支持文件上傳，只支持表單上傳，導(dǎo)致視頻大一點(diǎn)就會閃退。流上傳是上傳成功了，但是人家后臺不識別，這一次讓某平臺坑壞了。直接用file上傳，也傳過去了，上傳進(jìn)度100%了，但是人家那邊還是作為失敗處理，無奈！
言歸正傳，壓縮、導(dǎo)出視頻，需要通過AVAssetExportsession來實(shí)現(xiàn)，我們需要指定一個(gè)preset，并判斷是否支持這個(gè)preset，只有支持才能使用。
我們這里設(shè)置的preset為AVAssetExportPreset640x480，屬于壓縮得比較厲害的了，這需要根據(jù)服務(wù)器視頻上傳的支持程度而選擇的。然后通過調(diào)用異步壓縮并導(dǎo)出視頻：
- (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(@"目錄創(chuàng)建成功"); } else { NSLog(@"目錄創(chuàng)建失敗"); } } 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上有這么一樣bug：彈出錄制視頻頁面，再回來發(fā)現(xiàn)整個(gè)view都往下移動了，可能網(wǎng)上有很多解決辦法，下面只是其中一種：
[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：記得在選擇或者取消的代理中都調(diào)用！
新聞熱點(diǎn)
疑難解答
圖片精選
