Static kVTCompressionPropertyKey_BaseLayerBitRateFraction 

pub unsafe static kVTCompressionPropertyKey_BaseLayerBitRateFraction: &'static CFString

Available on crate feature VTCompressionProperties only.

This property indicates the desired bit rate fraction of the base layer

This is not a hard limit; the encoder will attempt to satisfy this ratio when possible. If not set, the encoder will manage the ratio. For example: If the target bitrate is set to 500kbps and kVTCompressionPropertyKey_BaseLayerBitRateFraction is set to 0.6, the base layer will be given a budget of 300kbps and the enhancement layer 200kbps.

See also Apple’s documentation