Why would you want to do something like that? Transcoding is always a bad idea because not only you lose quality because of the (possibly) decreased bitrate, but you also introduce additional quantization noise to the files.
Anyways, GX::Transcoder is a nice software that is dedicated to encoding and decoding.
Personally, I use the audio palyer foobar2000 that also comes with a converter that is able to encode to any format, as long as you have a command line encoder for the desired format (e.g. LAME.EXE for MP3).
Yep. I understand the audio issues, but, I have limited storage space and format support on my MP3 portable player. I want to create copies of specific tracks for download to the player.
I have made foobar2000 my default MP3, MPC and M3U player (once I wrestled automatic file re-associations away from MMJB). Very nice. Particularly appreciate the very wide coverage of file types and the tabbed playlists. Almost zero learning curve.
I have used GX::Transcoder to convert MPC to MP3 and tested it with some other transcoding. Took a bit to figure out the interface, but, once I had that done worked a charm.