As of 4.23, Matinee is no longer supported by UE4 and will be removed from the engine in the near future. Once removed, you will no longer be able to run a Matinee or open Matinee Editor.
Please use the Matinee to Sequencer Conversion Tool to convert any files to Sequencer as soon as possible.
The Matinee animation tool provides the ability to animate the properties of Actors over time, to create either dynamic gameplay or cinematic in-game sequences. The system is based on the use of specialized animation tracks in which you can place keyframes to set the values of certain properties of the Actors in the level. The Matinee Editor is similar to the non-linear editors used for video editing, making it familiar to video professionals.