I try to play in foorbar but doesn't work. Instead it open in media player classic.

Is it Musepack?

It's probably MPEG 1 Layer 2 audio - try to change the extension to mp2.

~ Florian

IIRC, mpa is a container for MPEG Audio, Layer-1 or Layer-2. Does fb2k support Layer-1?

Removed in one of the latest versions. Older versions do.

Edit: *cough* apparently support was removed over a year ago because there were no files to test with

I could provide some MP1 samples.

Hehe. Go to ReallyRareWares, grab SCMPX or SoloH or Uzura1. All these offer MP1 encoding. Uzura1 is actually an MP1-only encoder.

Isn't MPEG-1 Layer I what was called PASC in good ole' DCC days ?

Yes. Precision Adaptive Subband Coding.