Something like this might come in handy
On your matinee window, there is a movie button on the top right corner. When you click on it, you will get different settings that you can adjust for your recordings. When you are ready to record, hit ok. A new game window will pop up and your recording will start.Your recording will be saved in “…\Unreal Projects\Project_NAME\Saved…” There should be a folder there called videos or movies or something along those lines.
Your matinee needs to be called in your level blueprint .
select the matinee actor from the scene and open your level blueprint.
Create an “Event Begin Play” event.
After doing this right click and search for “Play” (Make sure your matinee actor is selected in the scene before doing this) and create the play node.
Connect the Event Begin Play to the play node. Open your matinee, make sure that U have a director track with a keyframe(hope U know what a director track is) setup to the camera you want to record.
Click the movie button on the top right corner and hit play.
Something like this.