How can I use ffmpeg to change the frame rate of a video file?

To change the frame rate of a video file using ffmpeg, you can use the following command:

ffmpeg -i input.mp4 -r 30 output.mp4

In this command, replace "input.mp4" with the name of your input video file and "output.mp4" with the desired name of your output video file. The "-r 30" flag specifies the new frame rate you want to set, in this case, 30 frames per second.