Is the n (ㄴ) pronounced in -ㅂ니다 endings?

Question

I'm just beginning to learn Korean, and, in the limited audio I'm hearing of pronunciations of -ㅂ니다 , I can't tell whether the /n/ sound is or should be pronounced. I'd like to learn to pronounce as properly as possible, though I also want to know about any different pronunciations in different contexts (casual, slang, polite, formal, etc.), so I won't get confused when hearing it, and possibly also be able to use the appropriate pronunciation for a given context.

Sometimes I think I hear /mnida/, sometimes I think I hear /mːida/ or just /mida/.

Perhaps it's just sometimes there, sometimes not, depending on how quickly the speaker is speaking?

Please link to examples

Duolingo; forvo.com; TTS in Anki (Android)

https://forvo.com/word/%EA%B0%90%EC%82%AC%ED%95%A9%EB%8B%88%EB%8B%A4/#ko

Answer 1

Your observation is right. In casual cases, it is sometimes pronounced as '~ㅁ다' (mda) instead of the proper '~ㅂ니다'. This could be seen as one of the nasalization case.
However this is not the 'right' pronunciation, so it is never used in any formal, official, or any kind of 'difficult' situations.

Answer 2

Yes, there is frequent "omission" (or syncope) of the 니 syllable in -ㅂ니다 endings, resulting in -ㅁ다. You may even see it in some subtitling for variety shows (which are known for their own textual liberties: use of Seoul dialect / 애교-related 'cute' verbal endings 여 and 구, loss of the first -이- in the copula -입니다).

Like many such omissions and abbreviations, it is part of fluent rapid speech, but its written form is not permitted in formal contexts. The 'speech level' implied by -ㅂ니다 itself is formal and polite, but many expressions using this speech level (such as 감사합니다 and 죄송합니다) are commonly used in the informal polite (해요체) and informal non-polite levels (해체) too. As such, expressions with -ㅂ니다 are often said at a fast pace in a relaxed setting, and syncope is fairly natural, even if it is considered somewhat casual.

Note that this does not extend to other endings with a medial -니- after a consonant. For example, the formal polite interrogative verbal ending -ㅂ니까 would simply sound 'wrong' and be misinterpreted as something else; or it might be possibly ambiguous in its formality (perhaps confusion with -ㄴ가, a written 반말 form).