Welcome to the world of audiocoding – AudioCoding.com. I use MP3 for compatibility, Ogg Vorbis for playback on PCs and Flac for archiving music files.
Here’s another resrouces, Audiocoding.com is doing free MPEG-4 encoders including HE MPEG-4 also know as AACplus. This is a very high compression codec. Got to give it a try from my friends at Coding Technologies