ffmpeg is a Command Line Interfacetool which can modify video and audio files.
To compress a video and reduce file size, try encoding with h265:
ffmpeg -i input.mp4 -vcodec libx265 -crf 28 output.mp4
Create a High-Quality GIF from a Video
ffmpeg -i input.mp4 -vf "fps=10,scale=920:-1:flags=lanczos" output.gif