get brightness value from CMSampleBuffer

BrightnessValue.swift

func getBrightnessValue(from sampleBuffer: CMSampleBuffer) -> Float {
  guard
      let metadataDict = CMCopyDictionaryOfAttachments(nil, sampleBuffer, kCMAttachmentMode_ShouldPropagate) as? [String: Any],
      let exifMetadata = metadataDict[String(kCGImagePropertyExifDictionary)] as? [String: Any],
      let brightnessValue = exifMetadata[String(kCGImagePropertyExifBrightnessValue)] as? Float
      else { return 0.0 }

  return brightnessValue
}