手把手教你实现微信小视频iOS代码实现

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 = 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 == 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 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 == 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，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, // 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, 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;
      //   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 > 0) {
         @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。

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

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