CITROEN DS4 Owner's Handbook Manual page 368

04 AUDIO
CD, USB
Information and advice
The audio system will only play fi les with extension ".mp3" or ".wma"
and a compression rate that is constant or variable between 32 Kbps
and 320 Kbps.
It is advisable to restrict fi le names to 20 characters without using
special characters (e.g. " ? ; ù) to avoid any playing or displaying
problems.
The playlists accepted are types .m3u and .pls.
The number of fi les is limited to 5 000 in 500 directories on a
maximum of 8 levels.
On a single disc, the CD player can read up to 255 MP3 fi les spread
over 8 directory levels. However, it is recommended that this be kept
to 2 levels so as to limit the time taken to access and play the CD.
During play, the folder structure is not observed.
In order to be able to play a recorded CDR or CDRW, when recording
it is preferable to select standards ISO 9660 level 1.2 or Joliet.
If the disc is recorded in another format, it may not be played correctly.
It is recommended that the same recording standard is always used
for an individual disc, with as low a speed as possible (4x maximum)
for optimum sound quality.
In the particular case of a multi-session CD, the Joliet standard is
recommended.
Do not connect a hard disk or USB device other than audio players to
the USB port. This may cause damage to your installation.