I just bought a car with pioneer f90bt unit in it. May be I am a bit dumb but how to play mp3/mp4 file from sd card? Does it need to be in a particular file or I have to download something to my sd card in order to load my mp3/mp4? coz I just put some files in my sd card, put into the slot and it just says 'now loading' but can't play at all. Thank you for your help