Recently I played with mencoder to convert several mpeg’s to one flv.
First concatenating the mpeg’s into one:
cat file1.mpeg file2.mpeg > file3.mpeg
Convert to flv:
ffmpeg -i file3.mpeg -deinterlace -ar 44100 -r 25 -qmin 15 -qmax 16 file1.flv
Just play with the qmax and qmin parameters for quality and filesize. Keep in mind that where qmin and qmax are decreased quality and filesize are dropping.
A third mpeg was rotated during capture. Using mencoder it is easy to rerotate a videofragment:
mencoder -ovc lavc -lavcopts vcodec=mjpeg -vf rotate=1 -oac copy file1.mpeg -o file4-rotated.mpeg