Static kVTCompressionPropertyKey_SuggestedLookAheadFrameCount 

pub unsafe static kVTCompressionPropertyKey_SuggestedLookAheadFrameCount: &'static CFString

Available on crate feature VTCompressionProperties only.

Requests that the encoder retain the specified number of frames during encoding. These frames will be used for additional analysis and statistics gathering before the frame is finally encoded at the end of the window. When this property is not set, video encoder will automatically determine the number of lookahead frames.

Encoder will choose number of lookahead frames closer to the suggested value based on internal configuration. This property directly affects latency of the video encoder. The following properties also affect look ahead frames:

1. Value of this property must be less than or equal to kVTCompressionPropertyKey_MaxFrameDelayCount.
2. This property is ignored when VTVideoEncoderSpecification_EnableLowLatencyRateControl is set to true
3. This property is ignored when kVTCompressionPropertyKey_Quality is set to 1.0
4. This property can not be used in conjunction with multi-pass feature (kVTCompressionPropertyKey_MultiPassStorage)

See also Apple’s documentation