I'm a big fan of using VBR for MP3s. I use FFMPEG to convert video (and sometimes audio) files to different formats. If you want to utilize VBR with LAME when you do FFMPEG conversions you need to specify the libmp3lame encoder, and then a given quality level:

ffmpeg -i input.wav -codec:a libmp3lame -qscale:a 2 output.mp3

ffmpeg -i video.mp4 -codec:a libmp3lame -qscale:a 6 /tmp/output.mkv