run mplayer on the command line and it will tell you, what codec it is using.
Playing <too bad, I had to censor that :)>.mpg.
MPEG-PS file format detected.
VIDEO: MPEG1 352x240 (aspect 12) 29,970 fps 1150,0 kbps (143,8 kbyte/s)
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
MP3lib: init layer2&3 finished, tables done
AUDIO: 44100 Hz, 2 ch, 16 bit (0x10), ratio: 28000->176400 (224,0 kbit)
Selected audio codec: [mp3] afm:mp3lib (mp3lib MPEG layer-2, layer-3)
It is not as comfortable as right clicking, but the information is there. There might be another way (using the gui, maybe).
Is that good enough? Have fun,