We're converting some old RM (RealMedia) files to use Flash instead; most are video but a small number are audio-only. To get these to work with the JW Flash Player, I used MediaCoder to convert the files. The container to use is M4A, as discussed in this thread. Here are the settings in MediaCoder:
Start by setting the video to off. Then change the audio settings; note that we set the audio container to MP4. MediaCoder automatically resolves this to M4A for audio-only files:
And finally set the main container type to Default.