How to add freeze frame to a video using ffmpeg
Assume there are three pauses of 3 seconds each at 5s, 12s and 20s of the original video. Here's the basic form of the command,

ffmpeg -i in -vf "setpts='PTS-STARTPTS + gte(T,5)*(3/TB) + gte(T,12)*(3/TB) + gte(T,20)*(3/TB)'" -af "asetpts='PTS-STARTPTS + gte(T,5)*(3/TB) + gte(T,12)*(3/TB) + gte(T,20)*(3/TB)',aresample=async=1:first_pts=0" -vsync cfr out