ArcGIS Pro 2.7 API Reference Guide
CreateKeyframe Method (LayerTrack)
Example 

ArcGIS.Desktop.Mapping Namespace > LayerTrack Class : CreateKeyframe Method
The layer associated with the keyframe.
The time at which to insert the keyframe in the track.
A value indicating if the layer is visible.
The value of the transparency.
The transition for the transparency of the layer. In the UI the default is ArcGIS.Core.CIM.AnimationTransition.Linear.
Create a new keyframe.
Syntax
Public Function CreateKeyframe( _
   ByVal layer As Layer, _
   ByVal atTime As TimeSpan, _
   ByVal isVisibile As Boolean, _
   ByVal transparency As Double, _
   ByVal transition As AnimationTransition _
) As Keyframe

Parameters

layer
The layer associated with the keyframe.
atTime
The time at which to insert the keyframe in the track.
isVisibile
A value indicating if the layer is visible.
transparency
The value of the transparency.
transition
The transition for the transparency of the layer. In the UI the default is ArcGIS.Core.CIM.AnimationTransition.Linear.
Remarks
If a keyframe already exists at that time it will be overwritten. The time is rounded to the nearest millisecond.
Example
Create a new layer keyframe.
public void CreateLayerKeyframe(Layer layer, double transparency, TimeSpan atTime)
{
  var mapView = MapView.Active;
  if (mapView != null)
    return;

  var animation = mapView.Map.Animation;
  var layerTrack = animation.Tracks.OfType<LayerTrack>().First(); //There will always be only 1 LayerTrack in the animation.
  layerTrack.CreateKeyframe(layer, atTime, true, transparency, ArcGIS.Core.CIM.AnimationTransition.Linear);
}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

LayerTrack Class
LayerTrack Members