The below joins audio and video streams into one MPEG1 or 2 file.
mplex -f 3 -o [output].mpg [input].m2v [input].mp2
Options for -f: 0 = Generic MPEG1, 1 = VCD, 2 = user-rate VCD, 3 = Generic MPEG2, 4 = SVCD, 5 = user-rate SVCD 6 = VCD Stills, 7 = SVCD Stills, 8 = DVD with NAV sectors, 9 = DVD