When you extract music from a CD onto a computer, it must be stored in a specific audio format. The default format used by Rhythmbox is Ogg Vorbis (.ogg or .oga). This is explained in the section called “Extract from a CD”.

Not all portable audio players are able to play files in the Ogg Vorbis format; for example, iPods cannot play this format. In order for your player to recognize your songs, you must convert them to a format which it supports. Nearly every player on the market supports the MP3 format, so this is usually a safe bet.

You can convert existing audio files to other formats using Sound Converter. The output format can be selected in the Sound Converter preferences.

You can change the default file format used by Rhythmbox when copying CDs. Click Edit → Preferences → Music and change the Preferred Format to the format of your choice. In future, all CDs copied to your computer will be copied in this format.