This is the description of the Skald's Raging Song (Su) class feature:
If a raging song affects allies, when the skald begins a raging song and at the start of each ally’s turn in which they can hear the raging song, the skald’s allies must decide whether to accept or refuse its effects. This is not an action. Unconscious allies automatically accept the song. If accepted, the raging song’s effects last for that ally’s turn or until the song ends, whichever comes first.
While under the effects of inspired rage, allies other than the skald cannot use any Charisma-, Dexterity-, or Intelligence-based skills (except Acrobatics, Fly, Intimidate, and Ride) or any ability that requires patience or concentration.
Does it prevent spellcasting?
The d20pfsrd entry has a link on the word "concentration" going to the Concentration Rules for spellcasters. But if read on paper, you could argue whether "an ability that requires concentration" equals spellcasting or whether you would need a Concentration Check to cast a spell while under the influence of a Raging Song.