Importing PCM Data

I’ve been playing around with MPG123 and also a little bit with Audacity. I took an MP3 file and I used Audacity to produce a pcm file and MPG123 to do the same.
However the files have differed greatly even taking into account the two files are pure pcm data, rather than wav. Are there any additions that need to be made to the pcm steam and can this be done easily?
I’m using VS2015 and windows 7

It’s not unusual for Audacity to not support every single metadata flag. Could that be it? Some of those flags can contain tons of data.


I don’t know the answer, but I see there are some examples in the mpg123 documentation that maybe helpful:

So meta is required then by sounds of it?