This is a program to mux RealMedia files.
It can for example combine audio from one file and video from other.
It can also extract audio or video from the file.
Also avaible is a beta version that can extract streams from SureStream files.
It accepts only RM and RMVB files, but you can try converting other formats into RM using dtdrive. I converted OGG into RM and then successfuly muxed it into RMVB.
The archive also contain a comand line version.
The program is currently awaible to download at
http://elwood.webz.cz/RMMuxer.zip
The SureStream beta
http://elwood.webz.cz/SureStreamBeta.zip