"They are talking about music."
Translation:Ils parlent de musique.
It is not "parlant".
In English, to mean that an action is in progress at the time you speak, you use the continuous verbal form, ie verb BE + action verb in the gerund form (-ing). o they are talking means they currently talk
In French, this verbal form does not exist (directly translated “they are parlant” is incorrect).
Therefore, you can translate either “ils/elles parlent” or “ils/elles sont en train de parler”, where the construction verb être + en train de + infinitive correctly expresses the English continuous form.