U010 – How do I convert my .mp3 audio files to .m4a for use in widgets?
Mp3 audio files are supported in our widgets, but not in iBooks. If you're creating widgets for use in iBooks, you should convert your audio files to .m4a before inserting them in your widget.
The easiest way to convert is to use iTunes.
Note that if you want to use the widget on an iPad / in iBooks, you should use an AAC audio encoding, 8-320 Kbps, 48 Khz stereo.
The online translator which pops up when searching for .mp3 to .m4a conversion uses the ALAC encoding should not be used as the format is not broadly supported.