Static kVTCompressionPropertyKey_CalculateMeanSquaredError 

pub unsafe static kVTCompressionPropertyKey_CalculateMeanSquaredError: &'static CFString

Available on crate feature VTCompressionProperties only.

This property requests that the encoder measure and output the Mean Squared Error(MSE) quality metric.

The MSE value returned may be measured using an internal representation of the decoded frame which may lack filtering or processing present in the actual decoded frame. Because of this, there may be a small delta between the reported MSE and the true MSE. If supported, the MSE values will be returned as sample buffer attachments on the encoded frame using the kVTSampleAttachmentKey_QualityMetrics key.

See also Apple’s documentation