What is the purpose of the 'fpsmode' parameter in ffmpeg and how can it be utilized to control the frame rate of a video during encoding or decoding processes?

The 'fpsmode' parameter in ffmpeg is used to control the frame rate of a video during encoding or decoding processes. It allows users to specify how the frames should be processed, such as by duplicating or dropping frames to achieve a desired frame rate. This parameter can be utilized to ensure smooth playback, adjust the speed of the video, or match the frame rate of the output to a specific standard.