手把手教你实现微信小视频iOS代码实现

2020-07-26 03:15:36

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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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