Variable bit rate
A method that dynamically allocates bitrate according to scene complexity within the overall target bitrate
ffmpeg -rc vbr -b:v 750k -maxrate 750k -bufsize 1500k
Two-pass VBR
Multi-pass encoding where the first pass analyzes scenes and the second pass optimizes bit allocation to balance file size and quality
ffmpeg -rc vbr -multipass 1 -b:v 750k -maxrate 750k -bufsize 1500k -an -f null ; \ ffmpeg -rc vbr -multipass 2 -b:v 750k -maxrate 750k -bufsize 1500k