All the media players do not support all audio formats. For this, we may need to convert from one format to another. The following step describe how we can do this, and is applicable to almost all formats.
Check out my post at Conversion From One Audio Format To Another Using Mencoder. If this doesn't help, you can follow the steps given below.
Using Shell Script
1. Open the terminal, and type,
varsha@varsha-laptop:~$ cd ~/.gnome2/nautilus-scripts
2. Open a new script,
varsha@varsha-laptop:~/.gnome2/nautilus-scripts$ gedit convert\ any\ to\ mp3.sh
3. Type the following code in the file.
mplayer -ao pcm "$1" -ao pcm:file=temp.wav
lame -b 128 temp.wav "$OUTNAME"
4. Comment out rm temp.wav if you do not want to remove the temporary file temp.wav, by prepending the line with a #. So,
5. Save the file and close the editor.
6. To convert any file to mp3, right-click the file and select Scripts-> convert any to mp3.sh.