iOS拍個小視訊

• 需求

  公司混合開發，uni端拍小視訊不是很理想，為達到仿微信效果，原生外掛走起

• 思路

  第1步：1個AVCaptureSession, 1塊AVCaptureVideoPreviewLayer[考慮相容替換成AVPreView]

  第2步：視訊錄製需video & audio, 需要對應的AVCaptureDeviceInput，同理對應的AVCaptureVideoDataOutput與AVCaptureAudioDataOutput

  第3步：代理中設定output區分video與audio, 並將對應的CMSampleBufferRef寫入到視訊檔案中

  第4步：寫入視訊檔案中，用到AVAssetWriter, 對應video & audio 需兩個AVAssetWriterInput, 加入AVAssetWriter

  第5步：CMSampleBufferRef不斷過來，AssetWriter不斷寫入，直到停止

• 上菜

  第一步的初始化就不寫了，沒事可以翻看本人前面的部落格

  第2步：兩個AVCaptureDeviceInput 兩個Output, 且設定Output的代理

  self.videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:device error:&error];
  if (error) {
      NSLog(@"取得裝置攝入videoInput物件時出錯, 錯誤原因: %@", error);
      return;
  }
  
  // 裝置新增到會話中
  if ([self.session canAddInput:self.videoInput]) {
      [self.session addInput:self.videoInput];
  }
  
  [self.videoOutput setSampleBufferDelegate:self queue:self.videoQueue];
  if ([self.session canAddOutput:self.videoOutput]) {
      [self.session addOutput:self.videoOutput];
  }
  
  // 音訊相關
  AVCaptureDevice *adevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
  self.audioInput = [[AVCaptureDeviceInput alloc] initWithDevice:adevice error:&error];
  
  if ([self.session canAddInput:self.audioInput]) {
      [self.session addInput:self.audioInput];
  }
  
  [self.audioOutput setSampleBufferDelegate:self queue:self.videoQueue];
  if ([self.session canAddOutput:self.audioOutput]) {
      [self.session addOutput:self.audioOutput];
  }
  
  // 視訊輸出
  - (AVCaptureVideoDataOutput *)videoOutput {
      if (!_videoOutput) {
          _videoOutput = [[AVCaptureVideoDataOutput alloc] init];
          _videoOutput.alwaysDiscardsLateVideoFrames = YES;
      }
      return _videoOutput;
  }
  
  // 音訊輸出
  - (AVCaptureAudioDataOutput *)audioOutput {
      if (!_audioOutput) {
          _audioOutput = [[AVCaptureAudioDataOutput alloc] init];
      }
      return _audioOutput;
  }
  
  

  第3步：啟動Session，代理裡面操作CMSampleBufferRef

  #pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate & AVCaptureAudioDataOutputSampleBufferDelegate
  - (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
      @autoreleasepool {
          // 視訊
          if (connection == [self.videoOutput connectionWithMediaType:AVMediaTypeVideo]) {
              if (!self.manager.outputVideoFormatDescription) {
                  @synchronized(self) {
                      CMFormatDescriptionRef formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer);
                      self.manager.outputVideoFormatDescription = formatDescription;
                  }
              } else {
                  @synchronized(self) {
                      if (self.manager.state == StateRecording) {
                          [self.manager appendBuffer:sampleBuffer type:AVMediaTypeVideo];
                      }
                  }
              }
          }
          
          //音訊
          if (connection == [self.audioOutput connectionWithMediaType:AVMediaTypeAudio]) {
              if (!self.manager.outputAudioFormatDescription) {
                  @synchronized(self) {
                      CMFormatDescriptionRef formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer);
                      self.manager.outputAudioFormatDescription = formatDescription;
                  }
              }
              @synchronized(self) {
                  if (self.manager.state == StateRecording) {
                      [self.manager appendBuffer:sampleBuffer type:AVMediaTypeAudio];
                  }
              }
          }
      }
  }
  

  第4步：AVAssetWriter以及對應的Input

  // writer初始化
  self.writer = [AVAssetWriter assetWriterWithURL:_videoUrl fileType:AVFileTypeMPEG4 error:nil];
  
  _videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:_videoSettings];
  //expectsMediaDataInRealTime 必須設為yes，需要從capture session 實時獲取資料
  _videoInput.expectsMediaDataInRealTime = YES;
  
  _audioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:_audioSettings];
  _audioInput.expectsMediaDataInRealTime = YES;
  
  if ([_writer canAddInput:_videoInput]) {
      [_writer addInput:_videoInput];
  }
  if ([_writer canAddInput:_audioInput]) {
      [_writer addInput:_audioInput];
  }
  

  第5步：第3步的CMSampleBufferRef通過AVAssetWriter寫入到視訊檔案中

  - (void)appendBuffer:(CMSampleBufferRef)buffer type:(NSString *)mediaType {
      if (buffer == NULL) {
          NSLog(@"empty sampleBuffer");
          return;
      }
      
      @synchronized (self) {
          if (self.state < StateRecording) {
              NSLog(@"not ready yet");
              return;
          }
      }
      
      CFRetain(buffer);
      dispatch_async(self.queue, ^{
          @autoreleasepool {
              @synchronized (self) {
                  if (self.state > StateFinish) {
                      CFRelease(buffer);
                      return;
                  }
              }
              
              if (!self.canWrite && mediaType == AVMediaTypeVideo) {
                  [self.writer startWriting];
                  [self.writer startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStamp(buffer)];
                  self.canWrite = YES;
              }
              
              if(!self.timer) {
                  dispatch_async(dispatch_get_main_queue(), ^{
                      self.timer = [NSTimer scheduledTimerWithTimeInterval:TIMER_INTERVAL target:self selector:@selector(updateProgress) userInfo:nil repeats:YES];
                      [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
                  });
              }
              
              // 寫入視訊資料
              if (mediaType == AVMediaTypeVideo) {
                  if (self.videoInput.readyForMoreMediaData) {
                      BOOL success = [self.videoInput appendSampleBuffer:buffer];
                      if (!success) {
                          @synchronized (self) {
                              [self stop:^{}];
                              [self destroy];
                          }
                      }
                  }
              }
              
              // 寫入音訊資料
              if (mediaType == AVMediaTypeAudio) {
                  if (self.audioInput.readyForMoreMediaData) {
                      BOOL success = [self.audioInput appendSampleBuffer:buffer];
                      if (!success) {
                          @synchronized (self) {
                              [self stop:^{}];
                              [self destroy];
                          }
                      }
                  }
              }
              CFRelease(buffer);
          }
      });
  }
  
  

• 寫在末尾：

  1. AVAssetWriterInput設定視訊屬性時，按照自己的需要設計，其中位元速率與幀率的設定會影響到拍攝後視訊的質量與大小，具體看各自專案的要求

  2. 如果視訊視角存在問題，可以從三個方向入手調整

     1.layer的connect設定下videoOrientation

     2.AVCaptureOutput的connect設定下videoOrientation

     3.AVAssetWriterInput針對video是設定下transform，比如Rotation M_PI/2 角度