If you have a video that does not need sound, like a background video on a web page, you can remove the sound with ffmpeg and the -an flag. This will help reduce file size.
ffmpeg -i [input_file] -vcodec copy -an [output_file]From the documentation:
The presence of -an disables audio stream selection
See on Stackoverflow and official documentation.
You can also output audio and video separately:
ffmpeg -i input.mp4 -map 0:0 -c:v copy only_video.mp4
ffmpeg -i input.mp4 -map 0:1 -c:a copy only_audio.mp4
This snippet from Stack overflow