[iOS]手把手教你实现微信小视频

　　本文个人原创，转载请注明出处，谢谢。

　　前段时间项目要求需要在聊天模块中加入类似微信的小视频功能，这边博客主要是为了总结遇到的问题和解决方法，希望能够对有同样需求的朋友有所帮助。

　　效果预览：

　　这里先罗列遇到的主要问题：　　

1. 视频剪裁  微信的小视频只是取了摄像头获取的一部分画面
2. 滚动预览的卡顿问题  AVPlayer播放视频在滚动中会出现很卡的问题

接下来让我们一步步来实现。

Part 1 实现视频录制

　　1.录制类WKMovieRecorder实现

　　创建一个录制类WKMovieRecorder，负责视频录制。

@interface WKMovieRecorder : NSObject

+ (WKMovieRecorder*) sharedRecorder;

- (instancetype)initWithMaxDuration:(NSTimeInterval)duration;

@end

　　定义回调block

/**
 *  录制结束
 *
 *  @param info     回调信息
 *  @param isCancle YES:取消 NO:正常结束
 */
typedef void(^FinishRecordingBlock)(NSDictionary *info, WKRecorderFinishedReason finishReason);
/**
 *  焦点改变
 */
typedef void(^FocusAreaDidChanged)();
/**
 *  权限验证
 *
 *  @param success 是否成功
 */
typedef void(^AuthorizationResult)(BOOL success);

@interface WKMovieRecorder : NSObject
//回调
@property (nonatomic, copy) FinishRecordingBlock finishBlock;//录制结束回调
@property (nonatomic, copy) FocusAreaDidChanged focusAreaDidChangedBlock;
@property (nonatomic, copy) AuthorizationResult authorizationResultBlock;
@end

　　定义一个cropSize用于视频裁剪

@property (nonatomic, assign) CGSize cropSize;

　　接下来就是capture的实现了，这里代码有点长，懒得看的可以直接看后面的视频剪裁部分

　　录制配置：

　　

@interface WKMovieRecorder ()
<
AVCaptureVideoDataOutputSampleBufferDelegate,
AVCaptureAudioDataOutputSampleBufferDelegate,
WKMovieWriterDelegate
>

{
    AVCaptureSession* _session;
    AVCaptureVideoPreviewLayer* _preview;
    WKMovieWriter* _writer;
    //暂停录制
    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;//存储录制帧
@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

　　实例化方法：

+ (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 = .f;
    }

    return self;
}

- (instancetype)init
{
    self = [super init];
    if (self) {
        _maxDuration = CGFLOAT_MAX;
        _duration = .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,  ) );
    }
    return self;
}

　　2.初始化设置

　　初始化设置分别为session创建、权限检查以及session配置

　　1.session创建

　　

self.session = [[AVCaptureSession alloc] init];
self.result = CaptureAVSetupResultSuccess;

　　2.权限检查

　　

//权限检查
        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的配置不能在主线程, 需要自行创建串行线程。

　　3.1.1 获取输入设备与输入流

　　

　AVCaptureDevice *captureDevice = [[self class] deviceWithMediaType:AVMediaTypeVideo preferringPosition:AVCaptureDevicePositionBack];

  _captureDevice = captureDevice;

  NSError *error = nil;
  _videoDeviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:captureDevice error:&error];

  if (!_videoDeviceInput) {
   NSLog(@"未找到设备");
  }

　　3.1.2 录制帧数设置

　　帧数设置的主要目的是适配iPhone4，毕竟是应该淘汰的机器了

　　

　　　　　　　int frameRate;
            if ( [NSProcessInfo processInfo].processorCount ==  )
            {
                if ([self.session canSetSessionPreset:AVCaptureSessionPresetLow]) {
                    [self.session setSessionPreset:AVCaptureSessionPresetLow];
                }
                frameRate = ;
            }else{
                if ([self.session canSetSessionPreset:AVCaptureSessionPreset640x480]) {
                    [self.session setSessionPreset:AVCaptureSessionPreset640x480];
                }
                frameRate = ;
            }

            CMTime frameDuration = CMTimeMake( , frameRate );

            if ( [_captureDevice lockForConfiguration:&error] ) {
                _captureDevice.activeVideoMaxFrameDuration = frameDuration;
                _captureDevice.activeVideoMinFrameDuration = frameDuration;
                [_captureDevice unlockForConfiguration];
            }
            else {
                NSLog( @"videoDevice lockForConfiguration returned error %@", error );
            }

　　3.1.3 视频输出设置

　　视频输出设置需要注意的问题是：要设置videoConnection的方向，这样才能保证设备旋转时的显示正常。

　　　　　　  //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(@"无法添加视频输入到会话");
            }

　　3.1.4 音频设置

　　需要注意的是为了不丢帧，需要把音频输出的回调队列放在串行队列中

　　　　　　　//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];

　　还需要注意一个问题就是对于session的配置代码应该是这样的

[self.session beginConfiguration];

...配置代码

[self.session commitConfiguration];

　　由于篇幅问题，后面的录制代码我就挑重点的讲了。

　　3.2  视频存储

　　现在我们需要在AVCaptureVideoDataOutputSampleBufferDelegate与AVCaptureAudioDataOutputSampleBufferDelegate的回调中，将音频和视频写入沙盒。在这个过程中需要注意的，在启动session后获取到的第一帧黑色的，需要放弃。

　　3.2.1 创建WKMovieWriter类来封装视频存储操作

　　WKMovieWriter的主要作用是利用AVAssetWriter拿到CMSampleBufferRef，剪裁后再写入到沙盒中。

　　这是剪裁配置的代码，AVAssetWriter会根据cropSize来剪裁视频，这里需要注意的一个问题是cropSize的width必须是320的整数倍，不然的话剪裁出来的视频右侧会出现一条绿色的线

　　NSDictionary *videoSettings;
    if (_cropSize.height ==  || _cropSize.width == ) {

        _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，视频录制就完成了。

　　接下来需要解决的预览的问题了

Part 2 卡顿问题解决

　　1.1 gif图生成

　　通过查资料发现了这篇blog 介绍说微信团队解决预览卡顿的问题使用的是播放图片gif，但是博客中的示例代码有问题，通过CoreAnimation来播放图片导致内存暴涨而crash。但是，还是给了我一些灵感，因为之前项目的启动页用到了gif图片的播放，所以我就想能不能把视频转成图片，然后再转成gif图进行播放，这样不就解决了问题了吗。于是我开始google功夫不负有心人找到了，图片数组转gif图片的方法。

　　gif图转换代码

static void makeAnimatedGif(NSArray *images, NSURL *gifURL, NSTimeInterval duration) {
    NSTimeInterval perSecond = duration /images.count;

    NSDictionary *fileProperties = @{
                                     (__bridge id)kCGImagePropertyGIFDictionary: @{
                                             (__bridge id)kCGImagePropertyGIFLoopCount: @, // 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);
}

　　转换是转换成功了，但是出现了新的问题，使用ImageIO生成gif图片时会导致内存暴涨，瞬间涨到100M以上，如果多个gif图同时生成的话一样会crash掉，为了解决这个问题需要用一个串行队列来进行gif图的生成　　

　　1.2 视频转换为UIImages

　　主要是通过AVAssetReader、AVAssetTrack、AVAssetReaderTrackOutput 来进行转换

//转成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, );
        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;
            //     视频播放时，
            m_pixelFormatType = kCVPixelFormatType_32BGRA;
            // 其他用途，如视频压缩
            //    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];
            // 要确保nominalFrameRate>0，之前出现过android拍的0帧视频
            while ([strongSelf.reader status] == AVAssetReaderStatusReading && videoTrack.nominalFrameRate > ) {
                 @autoreleasepool {
                // 读取 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);
                });
            }
        });

}

　　在这里有一个值得注意的问题，在视频转image的过程中，由于转换时间很短，在短时间内videoBuffer不能够及时得到释放，在多个视频同时转换时任然会出现内存问题，这个时候就需要用autoreleasepool来实现及时释放

@autoreleasepool {
  // 读取 video sample
  CMSampleBufferRef videoBuffer = [videoReaderOutput copyNextSampleBuffer];
  　　if (!videoBuffer) {
      break;
     }

  　　[images addObject:[WKVideoConverter convertSampleBufferRefToUIImage:videoBuffer]];
  　　 CFRelease(videoBuffer);
 }

　　至此，微信小视频的难点(我认为的)就解决了，至于其他的实现代码请看demo就基本实现了，demo可以从这里下载，如果觉得对你有帮助的话，帮我star一下哟，感激不尽　　

资料：

　　UIImages转gif图  https://gist.github.com/sahara108/6772691

　　视频暂停录制 　http://www.gdcl.co.uk/2013/02/20/iPhone-Pause.html

　　视频crop绿边解决 http://stackoverflow.com/questions/22883525/avassetexportsession-giving-me-a-green-border-on-right-and-bottom-of-output-vide

　　视频裁剪：http://stackoverflow.com/questions/15737781/video-capture-with-11-aspect-ratio-in-ios/16910263#16910263

　　CMSampleBufferRef转image https://developer.apple.com/library/ios/qa/qa1702/_index.html

　　微信小视频分析 http://www.jianshu.com/p/3d5ccbde0de1

感谢以上文章的作者