Contributions that do not add directly to the code of the game would not be protected by copyrights for literary works, but these components could be covered if an audiovisual copyright is taken out. As for authorship rights, most contributors are employees and hence their work would be considered "work for hire", belonging not to them, but to their employer. Music is generally not created in-house by game developers; since third parties are hired, this may not result in a work for hire.