The app uses a segment of the video where the face is well drawn to repair the face in another segment of the video, making the latter more consistent with the former.
In the selected segments, the face must be visible at all times.
The app can handle videos with multiple faces as long as (a) the number of faces within the segments is always the same; (b) the relative position of persons remains the same (if the woman is to the left of the man, it must be so throughout).