前段時間項目要求需要在聊天模塊中加入類似微信的小視頻功能，這邊博客主要是為了總結(jié)遇到的問題和解決方法，希望能夠?qū)τ型瑯有枨蟮呐笥延兴鶐椭?/p>
效果預(yù)覽：
這里先羅列遇到的主要問題：
1.視頻剪裁 微信的小視頻只是取了攝像頭獲取的一部分畫面
2.滾動預(yù)覽的卡頓問題 AVPlayer播放視頻在滾動中會出現(xiàn)很卡的問題
接下來讓我們一步步來實現(xiàn)。
Part 1 實現(xiàn)視頻錄制
1.錄制類WKMovieRecorder實現(xiàn)
創(chuàng)建一個錄制類WKMovieRecorder，負責視頻錄制。
@interface WKMovieRecorder : NSObject+ (WKMovieRecorder*) sharedRecorder; - (instancetype)initWithMaxDuration:(NSTimeInterval)duration; @end
定義回調(diào)block
/** * 錄制結(jié)束 * * @param info 回調(diào)信息 * @param isCancle YES:取消 NO:正常結(jié)束 */typedef void(^FinishRecordingBlock)(NSDictionary *info, WKRecorderFinishedReason finishReason);/** * 焦點改變 */typedef void(^FocusAreaDidChanged)();/** * 權(quán)限驗證 * * @param success 是否成功 */typedef void(^AuthorizationResult)(BOOL success);@interface WKMovieRecorder : NSObject//回調(diào)@property (nonatomic, copy) FinishRecordingBlock finishBlock;//錄制結(jié)束回調(diào)@property (nonatomic, copy) FocusAreaDidChanged focusAreaDidChangedBlock;@property (nonatomic, copy) AuthorizationResult authorizationResultBlock;@end
定義一個cropSize用于視頻裁剪
@property (nonatomic, assign) CGSize cropSize;
接下來就是capture的實現(xiàn)了，這里代碼有點長，懶得看的可以直接看后面的視頻剪裁部分
錄制配置：
@interface WKMovieRecorder ()<AVCaptureVideoDataOutputSampleBufferDelegate,AVCaptureAudioDataOutputSampleBufferDelegate,WKMovieWriterDelegate>{ AVCaptureSession* _session; AVCaptureVideoPreviewLayer* _preview; WKMovieWriter* _writer; //暫停錄制 BOOL _isCapturing; BOOL _isPaused; BOOL _discont; int _currentFile; CMTime _timeOffset; CMTime _lastVideo; CMTime _lastAudio; NSTimeInterval _maxDuration;}// Session management.@property (nonatomic, strong) dispatch_queue_t sessionQueue;@property (nonatomic, strong) dispatch_queue_t videoDataOutputQueue;@property (nonatomic, strong) AVCaptureSession *session;@property (nonatomic, strong) AVCaptureDevice *captureDevice;@property (nonatomic, strong) AVCaptureDeviceInput *videoDeviceInput;@property (nonatomic, strong) AVCaptureStillImageOutput *stillImageOutput;@property (nonatomic, strong) AVCaptureConnection *videoConnection;@property (nonatomic, strong) AVCaptureConnection *audioConnection;@property (nonatomic, strong) NSDictionary *videoCompressionSettings;@property (nonatomic, strong) NSDictionary *audioCompressionSettings;@property (nonatomic, strong) AVAssetWriterInputPixelBufferAdaptor *adaptor;@property (nonatomic, strong) AVCaptureVideoDataOutput *videoDataOutput;//Utilities@property (nonatomic, strong) NSMutableArray *frames;//存儲錄制幀@property (nonatomic, assign) CaptureAVSetupResult result;@property (atomic, readwrite) BOOL isCapturing;@property (atomic, readwrite) BOOL isPaused;@property (nonatomic, strong) NSTimer *durationTimer;@property (nonatomic, assign) WKRecorderFinishedReason finishReason;@end實例化方法：
+ (WKMovieRecorder *)sharedRecorder{ static WKMovieRecorder *recorder; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ recorder = [[WKMovieRecorder alloc] initWithMaxDuration:CGFLOAT_MAX]; }); return recorder;}- (instancetype)initWithMaxDuration:(NSTimeInterval)duration{ if(self = [self init]){ _maxDuration = duration; _duration = 0.f; } return self;}- (instancetype)init{ self = [super init]; if (self) { _maxDuration = CGFLOAT_MAX; _duration = 0.f; _sessionQueue = dispatch_queue_create("wukong.movieRecorder.queue", DISPATCH_QUEUE_SERIAL ); _videoDataOutputQueue = dispatch_queue_create( "wukong.movieRecorder.video", DISPATCH_QUEUE_SERIAL ); dispatch_set_target_queue( _videoDataOutputQueue, dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_HIGH, 0 ) ); } return self;} 2.初始化設(shè)置
初始化設(shè)置分別為session創(chuàng)建、權(quán)限檢查以及session配置
1）.session創(chuàng)建
self.session = [[AVCaptureSession alloc] init];
self.result = CaptureAVSetupResultSuccess;
2）.權(quán)限檢查
//權(quán)限檢查 switch ([AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo]) { case AVAuthorizationStatusNotDetermined: { [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) { if (granted) { self.result = CaptureAVSetupResultSuccess; } }]; break; } case AVAuthorizationStatusAuthorized: { break; } default:{ self.result = CaptureAVSetupResultCameraNotAuthorized; } } if ( self.result != CaptureAVSetupResultSuccess) { if (self.authorizationResultBlock) { self.authorizationResultBlock(NO); } return; } 3）.session配置
session配置是需要注意的是AVCaptureSession的配置不能在主線程, 需要自行創(chuàng)建串行線程。
3.1.1 獲取輸入設(shè)備與輸入流
AVCaptureDevice *captureDevice = [[self class] deviceWithMediaType:AVMediaTypeVideo preferringPosition:AVCaptureDevicePositionBack]; _captureDevice = captureDevice; NSError *error = nil; _videoDeviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:captureDevice error:&error]; if (!_videoDeviceInput) { NSLog(@"未找到設(shè)備"); } 3.1.2 錄制幀數(shù)設(shè)置
幀數(shù)設(shè)置的主要目的是適配iPhone4，畢竟是應(yīng)該淘汰的機器了
int frameRate; if ( [NSProcessInfo processInfo].processorCount == 1 ) { if ([self.session canSetSessionPreset:AVCaptureSessionPresetLow]) { [self.session setSessionPreset:AVCaptureSessionPresetLow]; } frameRate = 10; }else{ if ([self.session canSetSessionPreset:AVCaptureSessionPreset640x480]) { [self.session setSessionPreset:AVCaptureSessionPreset640x480]; } frameRate = 30; } CMTime frameDuration = CMTimeMake( 1, frameRate ); if ( [_captureDevice lockForConfiguration:&error] ) { _captureDevice.activeVideoMaxFrameDuration = frameDuration; _captureDevice.activeVideoMinFrameDuration = frameDuration; [_captureDevice unlockForConfiguration]; } else { NSLog( @"videoDevice lockForConfiguration returned error %@", error ); } 3.1.3 視頻輸出設(shè)置
視頻輸出設(shè)置需要注意的問題是：要設(shè)置videoConnection的方向，這樣才能保證設(shè)備旋轉(zhuǎn)時的顯示正常。
//Video if ([self.session canAddInput:_videoDeviceInput]) { [self.session addInput:_videoDeviceInput]; self.videoDeviceInput = _videoDeviceInput; [self.session removeOutput:_videoDataOutput]; AVCaptureVideoDataOutput *videoOutput = [[AVCaptureVideoDataOutput alloc] init]; _videoDataOutput = videoOutput; videoOutput.videoSettings = @{ (id)kCVPixelBufferPixelFormatTypeKey : @(kCVPixelFormatType_32BGRA) }; [videoOutput setSampleBufferDelegate:self queue:_videoDataOutputQueue]; videoOutput.alwaysDiscardsLateVideoFrames = NO; if ( [_session canAddOutput:videoOutput] ) { [_session addOutput:videoOutput]; [_captureDevice addObserver:self forKeyPath:@"adjustingFocus" options:NSKeyValueObservingOptionNew context:FocusAreaChangedContext]; _videoConnection = [videoOutput connectionWithMediaType:AVMediaTypeVideo]; if(_videoConnection.isVideoStabilizationSupported){ _videoConnection.preferredVideoStabilizationMode = AVCaptureVideoStabilizationModeAuto; } UIInterfaceOrientation statusBarOrientation = [UIApplication sharedApplication].statusBarOrientation; AVCaptureVideoOrientation initialVideoOrientation = AVCaptureVideoOrientationPortrait; if ( statusBarOrientation != UIInterfaceOrientationUnknown ) { initialVideoOrientation = (AVCaptureVideoOrientation)statusBarOrientation; } _videoConnection.videoOrientation = initialVideoOrientation; } } else{ NSLog(@"無法添加視頻輸入到會話"); } 3.1.4 音頻設(shè)置
需要注意的是為了不丟幀，需要把音頻輸出的回調(diào)隊列放在串行隊列中
//audio AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio]; AVCaptureDeviceInput *audioDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error]; if ( ! audioDeviceInput ) { NSLog( @"Could not create audio device input: %@", error ); } if ( [self.session canAddInput:audioDeviceInput] ) { [self.session addInput:audioDeviceInput]; } else { NSLog( @"Could not add audio device input to the session" ); } AVCaptureAudioDataOutput *audioOut = [[AVCaptureAudioDataOutput alloc] init]; // Put audio on its own queue to ensure that our video processing doesn't cause us to drop audio dispatch_queue_t audioCaptureQueue = dispatch_queue_create( "wukong.movieRecorder.audio", DISPATCH_QUEUE_SERIAL ); [audioOut setSampleBufferDelegate:self queue:audioCaptureQueue]; if ( [self.session canAddOutput:audioOut] ) { [self.session addOutput:audioOut]; } _audioConnection = [audioOut connectionWithMediaType:AVMediaTypeAudio]; 還需要注意一個問題就是對于session的配置代碼應(yīng)該是這樣的
[self.session beginConfiguration];
...配置代碼
[self.session commitConfiguration];
由于篇幅問題，后面的錄制代碼我就挑重點的講了。
3.2 視頻存儲
現(xiàn)在我們需要在AVCaptureVideoDataOutputSampleBufferDelegate與AVCaptureAudioDataOutputSampleBufferDelegate的回調(diào)中，將音頻和視頻寫入沙盒。在這個過程中需要注意的，在啟動session后獲取到的第一幀黑色的，需要放棄。
3.2.1 創(chuàng)建WKMovieWriter類來封裝視頻存儲操作
WKMovieWriter的主要作用是利用AVAssetWriter拿到CMSampleBufferRef，剪裁后再寫入到沙盒中。
這是剪裁配置的代碼，AVAssetWriter會根據(jù)cropSize來剪裁視頻，這里需要注意的一個問題是cropSize的width必須是320的整數(shù)倍，不然的話剪裁出來的視頻右側(cè)會出現(xiàn)一條綠色的線
NSDictionary *videoSettings; if (_cropSize.height == 0 || _cropSize.width == 0) { _cropSize = [UIScreen mainScreen].bounds.size; } videoSettings = [NSDictionary dictionaryWithObjectsAndKeys: AVVideoCodecH264, AVVideoCodecKey, [NSNumber numberWithInt:_cropSize.width], AVVideoWidthKey, [NSNumber numberWithInt:_cropSize.height], AVVideoHeightKey, AVVideoScalingModeResizeAspectFill,AVVideoScalingModeKey, nil]; 至此，視頻錄制就完成了。
接下來需要解決的預(yù)覽的問題了
Part 2 卡頓問題解決
1.1 gif圖生成
通過查資料發(fā)現(xiàn)了這篇blog 介紹說微信團隊解決預(yù)覽卡頓的問題使用的是播放圖片gif，但是博客中的示例代碼有問題，通過CoreAnimation來播放圖片導(dǎo)致內(nèi)存暴漲而crash。但是，還是給了我一些靈感，因為之前項目的啟動頁用到了gif圖片的播放，所以我就想能不能把視頻轉(zhuǎn)成圖片，然后再轉(zhuǎn)成gif圖進行播放，這樣不就解決了問題了嗎。于是我開始google功夫不負有心人找到了，圖片數(shù)組轉(zhuǎn)gif圖片的方法。
gif圖轉(zhuǎn)換代碼
static void makeAnimatedGif(NSArray *images, NSURL *gifURL, NSTimeInterval duration) { NSTimeInterval perSecond = duration /images.count; NSDictionary *fileProperties = @{ (__bridge id)kCGImagePropertyGIFDictionary: @{ (__bridge id)kCGImagePropertyGIFLoopCount: @0, // 0 means loop forever } }; NSDictionary *frameProperties = @{ (__bridge id)kCGImagePropertyGIFDictionary: @{ (__bridge id)kCGImagePropertyGIFDelayTime: @(perSecond), // a float (not double!) in seconds, rounded to centiseconds in the GIF data } }; CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)gifURL, kUTTypeGIF, images.count, NULL); CGImageDestinationSetProperties(destination, (__bridge CFDictionaryRef)fileProperties); for (UIImage *image in images) { @autoreleasepool { CGImageDestinationAddImage(destination, image.CGImage, (__bridge CFDictionaryRef)frameProperties); } } if (!CGImageDestinationFinalize(destination)) { NSLog(@"failed to finalize image destination"); }else{ } CFRelease(destination);}轉(zhuǎn)換是轉(zhuǎn)換成功了，但是出現(xiàn)了新的問題，使用ImageIO生成gif圖片時會導(dǎo)致內(nèi)存暴漲，瞬間漲到100M以上，如果多個gif圖同時生成的話一樣會crash掉，為了解決這個問題需要用一個串行隊列來進行g(shù)if圖的生成
1.2 視頻轉(zhuǎn)換為UIImages
主要是通過AVAssetReader、AVAssetTrack、AVAssetReaderTrackOutput 來進行轉(zhuǎn)換
//轉(zhuǎn)成UIImage- (void)convertVideoUIImagesWithURL:(NSURL *)url finishBlock:(void (^)(id images, NSTimeInterval duration))finishBlock{ AVAsset *asset = [AVAsset assetWithURL:url]; NSError *error = nil; self.reader = [[AVAssetReader alloc] initWithAsset:asset error:&error]; NSTimeInterval duration = CMTimeGetSeconds(asset.duration); __weak typeof(self)weakSelf = self; dispatch_queue_t backgroundQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0); dispatch_async(backgroundQueue, ^{ __strong typeof(weakSelf) strongSelf = weakSelf; NSLog(@""); if (error) { NSLog(@"%@", [error localizedDescription]); } NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo]; AVAssetTrack *videoTrack =[videoTracks firstObject]; if (!videoTrack) { return ; } int m_pixelFormatType; // 視頻播放時， m_pixelFormatType = kCVPixelFormatType_32BGRA; // 其他用途，如視頻壓縮 // m_pixelFormatType = kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange; NSMutableDictionary *options = [NSMutableDictionary dictionary]; [options setObject:@(m_pixelFormatType) forKey:(id)kCVPixelBufferPixelFormatTypeKey]; AVAssetReaderTrackOutput *videoReaderOutput = [[AVAssetReaderTrackOutput alloc] initWithTrack:videoTrack outputSettings:options]; if ([strongSelf.reader canAddOutput:videoReaderOutput]) { [strongSelf.reader addOutput:videoReaderOutput]; } [strongSelf.reader startReading]; NSMutableArray *images = [NSMutableArray array]; // 要確保nominalFrameRate>0，之前出現(xiàn)過android拍的0幀視頻 while ([strongSelf.reader status] == AVAssetReaderStatusReading && videoTrack.nominalFrameRate > 0) { @autoreleasepool { // 讀取 video sample CMSampleBufferRef videoBuffer = [videoReaderOutput copyNextSampleBuffer]; if (!videoBuffer) { break; } [images addObject:[WKVideoConverter convertSampleBufferRefToUIImage:videoBuffer]]; CFRelease(videoBuffer); } } if (finishBlock) { dispatch_async(dispatch_get_main_queue(), ^{ finishBlock(images, duration); }); } }); }在這里有一個值得注意的問題，在視頻轉(zhuǎn)image的過程中，由于轉(zhuǎn)換時間很短，在短時間內(nèi)videoBuffer不能夠及時得到釋放，在多個視頻同時轉(zhuǎn)換時任然會出現(xiàn)內(nèi)存問題，這個時候就需要用autoreleasepool來實現(xiàn)及時釋放
@autoreleasepool { // 讀取 video sample CMSampleBufferRef videoBuffer = [videoReaderOutput copyNextSampleBuffer]; if (!videoBuffer) { break; } [images addObject:[WKVideoConverter convertSampleBufferRefToUIImage:videoBuffer]]; CFRelease(videoBuffer); }至此，微信小視頻的難點(我認為的)就解決了，至于其他的實現(xiàn)代碼請看demo就基本實現(xiàn)了，demo可以從這里下載。
視頻暫停錄制 http://www.gdcl.co.uk/2013/02/20/iPhone-Pause.html
視頻crop綠邊解決 http://stackoverflow.com/questions/22883525/avassetexportsession-giving-me-a-green-border-on-right-and-bottom-of-output-vide
視頻裁剪：http://stackoverflow.com/questions/15737781/video-capture-with-11-aspect-ratio-in-ios/16910263#16910263
CMSampleBufferRef轉(zhuǎn)image https://developer.apple.com/library/ios/qa/qa1702/_index.html
微信小視頻分析 http://www.jianshu.com/p/3d5ccbde0de1
感謝以上文章的作者
以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持VEVB武林網(wǎng)。
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