Learn Hardcore Norwegian: Pianisten spiller en rolig melodi for publikum. - The pianist plays a calm melody for the audience.

In Norwegian Bokmål you show “the” by adding a suffix to the noun. Since pianist is a common-gender noun, you add -en to make it definite singular:

pianist (a pianist) → pianisten (the pianist)

How do you form the indefinite and definite forms of pianist in both singular and plural?

Because pianist is common gender, you use en/-en in singular and -er/-ene in plural:

Indefinite singular: en pianist (a pianist)
Definite singular: pianisten (the pianist)
Indefinite plural: pianister (pianists)
Definite plural: pianistene (the pianists)

Why is it en rolig melodi and not ei rolig melodi?

In Bokmål almost all feminine and masculine nouns are treated as common gender and use en as the indefinite article. The form ei is mainly Nynorsk or dialectal. Since melodi is common gender, you say en melodi.

Why doesn’t the adjective rolig take a -t ending in en rolig melodi?

Adjectives in Norwegian have three forms:

Indefinite common gender (no ending)
Indefinite neuter (usually -t)
Definite (usually -e)

Because melodi is common gender and indefinite here, rolig stays in its base form (no -t).

What is the grammatical gender of melodi, and how does that affect article and adjective agreement?

melodi is common gender. That means:

Indefinite article: en (not et)
Adjective in indefinite common: base form (rolig)
Definite form would be den rolige melodien (adjective takes -e, noun takes -en).

Why is spiller used here instead of a continuous form like “is playing”?

Norwegian does not have a separate continuous aspect. The simple present tense (spiller) covers both habitual actions (“plays”) and ongoing actions (“is playing”).

Why is the preposition for used in for publikum? Could you say til publikum instead?

When you perform or dedicate something for an audience, Norwegian normally uses for just like English. til is more about direction (“to someone”) or giving something directly, and sounds less natural in this context.

Why is there no article before publikum? Could you say et publikum?

publikum is an invariable collective/mass noun borrowed from Latin. It doesn’t have an indefinite singular (et/en) or a plural form in ordinary use. You simply say publikum for “the audience.”

What happens to the word order if you start the sentence with for publikum?

Norwegian main clauses follow the V2 rule: the verb must be in second position. If you front for publikum, you invert subject and verb:

Original: Pianisten spiller en rolig melodi for publikum. (S-V-O-PP)
Fronted PP: For publikum spiller pianisten en rolig melodi. (PP-V-S-O)

How would you express “the calm melody” in the definite form?

You turn both the adjective and noun definite:

den (definite article for common gender) + rolige (adjective -e in definite) + melodien (noun -en in definite)
den rolige melodien