MEncoder can create MPEG (MPEG-PS) format output files. Usually, when you are using MPEG-1 or MPEG-2 video, it is because you are encoding for a constrained format such as SVCD, VCD, or DVD. The specific requirements for these formats are explained in the VCD and DVD creation guide section.
To change MEncoder's output file format, use the -of mpeg option.
Example:
mencoderinput.avi-of mpeg -ovc lavc -lavcopts vcodec=mpeg1video -oac copyother_options-ooutput.mpg
Creating an MPEG-1 file suitable to be played on systems with minimal multimedia support, such as default Windows installs:
mencoderinput.avi-of mpeg -mpegopts format=mpeg1:tsaf:muxrate=2000 -ooutput.mpg-oac lavc -ovc lavc \ -lavcopts acodec=mp2:abitrate=224:vcodec=mpeg1video:vbitrate=1152:keyint=15:mbd=2:aspect=4/3