Iphone 如何正确定位从AVCaptureVideoDataOutputSampleBufferDelegate生成的图像

我正在使用

AVCaptureVideoDataOutputSampleBufferDelegate

，收到一个

CMSampleBufferRef

，我将其转换为

UIImage

——但生成的图像方向不正确

// Get a CMSampleBuffer's Core Video image buffer for the media data
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
// Lock the base address of the pixel buffer
CVPixelBufferLockBaseAddress(imageBuffer, 0); 

// Get the number of bytes per row for the pixel buffer
void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

// Get the number of bytes per row for the pixel buffer
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
// Get the pixel buffer width and height
size_t width = CVPixelBufferGetWidth(imageBuffer); 
size_t height = CVPixelBufferGetHeight(imageBuffer); 

// Create a device-dependent RGB color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 

// Create a bitmap graphics context with the sample buffer data
CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
// Create a Quartz image from the pixel data in the bitmap graphics context
CGImageRef quartzImage = CGBitmapContextCreateImage(context); 
// Unlock the pixel buffer
CVPixelBufferUnlockBaseAddress(imageBuffer,0);

// Free up the context and color space
CGContextRelease(context); 
CGColorSpaceRelease(colorSpace);

// Create an image object from the Quartz image
UIImage *img = [UIImage imageWithCGImage:quartzImage];

// Release the Quartz image
CGImageRelease(quartzImage);

如果我在纵向模式下握住iPhone，生成的图像将旋转90度（逆时针）。 如果我将iPhone保持在横向左侧（主页按钮位于左侧），则生成的图像将向上。 如果我将iPhone保持在横向右侧（主页按钮位于右侧），则生成的图像是颠倒的

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我使用的是设备的前置摄像头-但我也将使用前置摄像头，因此生成的图像应始终具有正确的方向。

当我记录img.imageOrientation时，我始终获得0-UP