How to reduce a video's file size with ffmpeg

Using ffmpeg, you can easily re-encode a video to reduce its file size.

Command

Do it like this:

ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset slow -c:a copy -movflags +faststart output.mp4

Arguments

• -i input.mp4 specifies your input file
• -c:v libx264 specifies H.264 encoding.
  • Use -c:v libx265 for H.265/HEVC. It's an excellent modern encoding standard that is fairly widely supported, but not on older devices.
• -crf 23 specifies the Constant Rate Factor, i.e. video quality.
  • Lower values mean higher quality.
  • 23 produces some compression artifacts but is often good enough. Choose 20 if you want better quality with still reasonably small video files.
  • When using H.265/HEVC, you may use higher numbers since HEVC offers better overall compression.
• -preset slow for good compression with reasonably quick encoding duration.
• -c:a copy will copy the audio stream without re-encoding. It's usually not worth to re-encode at a lower audio quality.
• -movflags +faststart allows starting playback without downloading the entire file.
• output.mp4 specifies your output file