How to add image or movie to ofxVideoRecorder?

Hi, all.
I am using ofxVideoRecorder to an encode audio and video.
I’d like to add image on encode movie, and add movie or image sequences before or after encode movie.
After that, include these image or movie and output data as movie file.
How should I do…?

Environment:
Xcode 8.3.3
of_v0.9.8_osx_release