Slammin' Rap, the latest volume of an ongoing music ''magazine'' on videocassette starts out interestingly enough. An energetic L.L. Cool J discusses the importance of business savvy in an industry fueled by hype; he's followed by short segments on Schoolly D, an aggressively street- wise rapper from Philly, and Eric B. and Rakim, a New York duo who treat us to an a cappella rap. But it quickly degenerates, making the shortcomings of fanzines all too clear. There are long sequences of self-indulgent horsing around, the amateurish feel of wobbly camcorders and haphazard editing, and the distinct odor of self-promotion not to mention moronic sound bites from the likes of Hoes Wit Attitude, a dreadful trio of female rappers in spiked heels and string bikinis who proclaim: ''We're not selling sex, we're selling sexy!''
For hard-core fans and avid observers of hip-hop culture, this 60-minute commercial is varied enough to be watchable. But compared with a well-done primer like PBS' recent Rap City Rhapsody (which is not yet available on video), Slammin' Rap really does deserve a slam. D