unplug the device then do dmesg | grep usb
Take a look at the last few entries so you know what they are. (Probably something about the usb device being disconnected...)
plug the device back in again, then repeat
dmesg | grep usb
and post the differences.
(you can also pipe the output to text files and run the diff command on them.)
[4314341.650000] usb 2-3: new full speed USB device using ohci_hcd and address 2[4314343.415000] usb-storage: device found at 2
[4314343.415000] usb-storage: waiting for device to settle before scanning
[4314343.415000] usbcore: registered new driver usb-storage
[4314348.431000] usb-storage: device scan complete
... this is the sort of thing that corresponds to my device.
An intreguing idea would be to put some photos on it and see if the camera tool can import them... basically, if it is seen in the camera tool, then it has been mounted.
In my FC4 system, a device is created at /dev/sde (if I use the front panel socket) and it is automounted to /media/usbstick. I note that /dev has sda,b,c and d already, creating sde when I plug in.
/proc/bus/usb/devices shows 5 when plugged in and 4 when not - as expected.
[~]$ cat /proc/bus/usb/devices > unplugged
[~]$ cat /proc/bus/usb/devices > plugged
[~]$ diff plugged unplugged
> T: Bus=02 Lev=01 Prnt=01 Port=02 Cnt=01 Dev#= 3 Spd=12 MxCh= 0
> D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
> P: Vendor=10d6 ProdID=1100 Rev= 1.00
> S: Product=USB 2.0(FS) FLASH DISK
> S: SerialNumber=USB 2.0(FS) FLASH DISK
> C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
> I: If#= 0 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=05 Prot=50 Driver=usb-storage
> E: Ad=01(O) Atr=02(Bulk) MxPS= 64 Ivl=0ms
> E: Ad=82(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
... as you can see, my disk is identified. The "unknown" you are getting suggests that your device simple is not telling your computer what it is.
You may need to check with your dosumentation for your mp3 player. It is possible that it dosn't use a standard storage type. Or there may be some setting on the HW so it can be used as a storage device.
However - connection protocol matters. If it is regestering as a camera, then perhaps it is using PTP ... the documentation will tell you about connection types supported.
A puzzle, because all these players I've tried just look like a usb drive.
You could try the mount command on /dev/sda sdb etc until you get a hit. This is the traditional method.
mount -t vfat /dev/sda /media/usbstick