AVCapture appendSampleBuffer

Question

我要疯了 - 到处找，尝试了所有我能想到的东西。

我正在制作一个使用 AVFoundation 的 iPhone 应用程序 - 特别是 AVCapture 以使用 iPhone 摄像头捕捉视频。

我需要在录制的视频源上叠加一个自定义图像。

到目前为止，我已经设置了 AVCapture 会话，可以显示提要、访问框架、将其保存为 UIImage 并将覆盖图像添加到上面。然后将这个新的 UIImage 转换为 CVPixelBufferRef。为了仔细检查 bufferRef 是否正常工作，我将它转换回 UIImage，它仍然可以正常显示图像。

当我尝试将 CVPixelBufferRef 转换为 CMSampleBufferRef 以附加到 AVCaptureSessionsassetWriterInput 时，问题就开始了。当我尝试创建 CMSampleBufferRef 时，它总是返回 NULL。

这里是 -(void)captureOutput 函数

- (void)captureOutput:(AVCaptureOutput *)captureOutput 
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
    fromConnection:(AVCaptureConnection *)connection
{ 

 UIImage *botImage = [self imageFromSampleBuffer:sampleBuffer];
 UIImage *wheel = [self imageFromView:wheelView];

 UIImage *finalImage = [self overlaidImage:botImage :wheel];
 //[previewImage setImage:finalImage]; <- works -- the image is being merged into one UIImage

 CVPixelBufferRef pixelBuffer = NULL;
 CGImageRef cgImage = CGImageCreateCopy(finalImage.CGImage);
 CFDataRef image = CGDataProviderCopyData(CGImageGetDataProvider(cgImage));
 int status = CVPixelBufferCreateWithBytes(NULL,
             self.view.bounds.size.width,
             self.view.bounds.size.height,
             kCVPixelFormatType_32BGRA, 
             (void*)CFDataGetBytePtr(image), 
             CGImageGetBytesPerRow(cgImage), 
             NULL, 
             0,
             NULL, 
             &pixelBuffer);
 if(status == 0){
  OSStatus result = 0;

  CMVideoFormatDescriptionRef videoInfo = NULL;
  result = CMVideoFormatDescriptionCreateForImageBuffer(NULL, pixelBuffer, &videoInfo);
  NSParameterAssert(result == 0 && videoInfo != NULL);

  CMSampleBufferRef myBuffer = NULL;
  result = CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault,
            pixelBuffer, true, NULL, NULL, videoInfo, NULL, &myBuffer);
  NSParameterAssert(result == 0 && myBuffer != NULL);//always null :S

  NSLog(@"Trying to append");

  if (!CMSampleBufferDataIsReady(myBuffer)){
   NSLog(@"sampleBuffer data is not ready");
   return;
  }

  if (![assetWriterInput isReadyForMoreMediaData]){
   NSLog(@"Not ready for data :(");
   return;
  }

  if (![assetWriterInput appendSampleBuffer:myBuffer]){   
   NSLog(@"Failed to append pixel buffer");
  }



 }

}

我经常听到的另一个解决方案是使用 AVAssetWriterInputPixelBufferAdaptor，它消除了进行混乱的 CMSampleBufferRef 包装的需要。但是，我已经搜索了堆栈和苹果开发人员论坛和文档，但找不到关于如何设置或如何使用它的清晰描述或示例。如果有人有一个可行的例子，请给我看或帮我解决上述问题 - 一直在不停地研究这个问题一个星期，我束手无策。

如果您需要任何其他信息，请告诉我

提前致谢，

迈克尔

Answer 1

你需要 AVAssetWriterInputPixelBufferAdaptor，这里是创建它的代码：

    // Create dictionary for pixel buffer adaptor
NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA], kCVPixelBufferPixelFormatTypeKey, nil];

// Create pixel buffer adaptor
m_pixelsBufferAdaptor = [[AVAssetWriterInputPixelBufferAdaptor alloc] initWithAssetWriterInput:assetWriterInput sourcePixelBufferAttributes:bufferAttributes];

以及使用它的代码：

// If ready to have more media data
if (m_pixelsBufferAdaptor.assetWriterInput.readyForMoreMediaData) {
    // Create a pixel buffer
    CVPixelBufferRef pixelsBuffer = NULL;
    CVPixelBufferPoolCreatePixelBuffer(NULL, m_pixelsBufferAdaptor.pixelBufferPool, &pixelsBuffer);

    // Lock pixel buffer address
    CVPixelBufferLockBaseAddress(pixelsBuffer, 0);

    // Create your function to set your pixels data in the buffer (in your case, fill with your finalImage data)
    [self yourFunctionToPutDataInPixelBuffer:CVPixelBufferGetBaseAddress(pixelsBuffer)];

    // Unlock pixel buffer address
    CVPixelBufferUnlockBaseAddress(pixelsBuffer, 0);

    // Append pixel buffer (calculate currentFrameTime with your needing, the most simplest way is to have a frame time starting at 0 and increment each time you write a frame with the time of a frame (inverse of your framerate))
    [m_pixelsBufferAdaptor appendPixelBuffer:pixelsBuffer withPresentationTime:currentFrameTime];

    // Release pixel buffer
    CVPixelBufferRelease(pixelsBuffer);
}

别忘了释放你的 pixelBufferAdaptor。

Answer 2

我通过使用 CMSampleBufferCreateForImageBuffer() 来实现。

OSStatus ret = 0;
CMSampleBufferRef sample = NULL;
CMVideoFormatDescriptionRef videoInfo = NULL;
CMSampleTimingInfo timingInfo = kCMTimingInfoInvalid;
timingInfo.presentationTimeStamp = pts;
timingInfo.duration = duration;

ret = CMVideoFormatDescriptionCreateForImageBuffer(NULL, pixel, &videoInfo);
if (ret != 0) {
    NSLog(@"CMVideoFormatDescriptionCreateForImageBuffer failed! %d", (int)ret);
    goto done;
}
ret = CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault, pixel, true, NULL, NULL,
                                         videoInfo, &timingInfo, &sample);
if (ret != 0) {
    NSLog(@"CMSampleBufferCreateForImageBuffer failed! %d", (int)ret);
    goto done;
}