The bitrate with ffmpeg is a parameter that sets the quality of your video.
You can set the bitrate:
- directly by giving a value with b:v (if you care about the exact file size)
ffmpeg -i input_video.mp4 -b:v 10M output_video.mp4
- or indirectly by giving the Constant Rate Factor (CRF) of the encoding scheme 1)- if you want to retain good visual quality and don't care about the exact bitrate or filesize of the encoded file.