Static kVTSampleAttachmentKey_QualityMetrics 

pub unsafe static kVTSampleAttachmentKey_QualityMetrics: &'static CFString

Available on crate feature VTCompressionProperties only.

The value for this key contain quality-related metadata from the video encoder for a video frame.

The video encoder will attach this via the CMSampleBufferGetSampleAttachmentsArray interface before emitting the sample buffer.

See also Apple’s documentation