Frame rate must be constant and set to 23.98, 25 or 29.97 (based on native frame rate)
*Duplicate Frames is an issue that arises when a video shot at a certain frame rate, its native frame , is encoded at a different one. Most often seen when videos shot at 23.98 fps are encoded at 29.97 fps, the video adds in a doubled frame every four or five frames, for example, in order to make up for the change. This creates a stuttering effect that is bad for playback. In terms of a solution, you should provide original, unaltered version or a new file file must be reencoded at the native frame rate.