Bash and Single Quotes

[RGH]

I'm trying to write a shell script to convert video files using vlc and 
avidemux, and I've run into a problem. I need to be able to do something 
like this:

    vlc -v -I dummy $FIL 
--sout='#transcode{vcodec=dummy,acodec=mp3,ab=192}:std{access=file,mux=dummy,dst="$MP3"}' 
vlc://quit

But of course this doesn't work because the $MP3 variable doesn't get 
expanded in single quotes. The single quotes seem to need to be there to 
protect the "{", though. So, how can this be done?

Cheers,
rh