I'm brand new to learning Korean -- I have studied a little bit of Hangul to learn the sounds, and I just started Lesson 1 of Elementary Korean, 2nd ed. by King & Yeon.
In this lesson there is a list of basic expressions. I am confused in a couple of places where I see the letter ㅂ but the pronunciation guide clearly shows the pronunciation as "m". But in other places, the pronunciation of the same character is "p" or "b" as I would expect.
For example, in Lesson 1, basic expression 5:
...입니다. (English: I'm...)
the pronunciation is shown as "...imnida"
I looked in Sounds of Korean (Choo & O'Grady), but didn't find any rules for when ㅂ should be pronounced as "m" -- maybe I just missed it?
Note: I am trying to avoid Romanization; I only consulted it here when I noticed the discrepancy between what I was hearing on the audio and what I was seeing in Hangul.