How to split flv file by size using FFmpeg or mencoder or smth else?

Question

I need to split an flv file into chunks of the known size on linux server. For example my original file is 9Mb and the chunk size is 4Mb. So I should get 3 parts - 4Mb, 4Mb and

Answer 1

calculate ~time (sec) of every block & use -ss X -t X+avg_block_time for split video