Common uses for FFMPEG

Installation

On MacOS

brew install ffmpeg

Convert a weird file into a normal MP4

ffmpeg -i inputfile.mov  -movflags +faststart outputfile.mp4

Convert an animated gif into an MP4

We had to do this with the new launch of Lullabot.com

ffmpeg -i input-file.gif -movflags +faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" output-file.mp4

Compress a video file

ffmpeg -i input.mp4  -movflags +faststart -vcodec libx264  -crf 20 output.mp4

The 20 is the constant rate factor and should be between 18 and 28. The default is 23. According to the previously linked article, a change of ±6 should result in about half/double the file size, although your results might vary.