NoBIGTech Wiki Técnico

Source: https://unix.stackexchange.com/questions/28803/how-can-i-reduce-a-videos-size-with-ffmpeg

That answer was written in 2009. Nowadays (2020) a video format much better than H.264 is widely available, namely H.265 (better in that it compresses more for the same quality, or gives higher quality for the same size). To use it, replace the libx264 codec with libx265, and push the compression lever further by increasing the CRF value — add, say, 4 or 6, since a reasonable range for H.265 may be 24 to 30.

# slower, but better (H.264 codec)
ffmpeg -i input.mp4 -vcodec libx264 -crf 20 output.mp4
 
# even better compression with H.265
ffmpeg -i input.avi -vcodec libx265 -crf 20 output.avi
 
 
# faster, and more lossy compression
# depending on your needs, it could fit
ffprobe input.mp4
# 
# search for "bitrate:"
# example: 920 kb/s
# 50% of quality loss == 450 kb/s aprox
# 
# If you dont see any difference on lower bitrate, set it lower
# it will compress even more
ffmpeg -i input.mp4 -b:v 450k output.mp4
 
# faster, but less compression
ffmpeg -i input.mkv -vcodec copy -crf 20 output.mkv