Music videos began as promotional tools for songs but became an art form in their own right. Directors like Michel Gondry brought unique styles to videos in the 1990s. Samuel Bayer is known for directing alternative rock videos like Nirvana's "Smells Like Teen Spirit" and Green Day's "Jesus of Suburbia" which linked together themes. Conventions for metal music videos include dark themes, dark clothing, powerful poses from band members, and fast editing to match the intensity of the music.