meta/exif-data from captureStillImageAsynchronouslyFromConnection missing

When I capture still images with the captureStillImageAsynchronouslyFromConnection method of AVCaptureStillImageOutput together with the AVCaptureSessionPresetPhoto, trying to retrieve exif data with CMGetAttachment an开发者_运维百科d kCGImagePropertyExifDictionary from the CVImageBuffer gives back NULL. I especially need the ISO-rating of the last taken photo. How can I retrieve that information?

The problem was, that I used CMGetAttachment with the CVImageBuffer, but I had to use it with the CMSampleBuffer.