The rap performer-impresario Jay-Z doesn’t have the face of a music idol – his looks are those of an ordinary guy, somewhere between handsome and homely.

But the look in his eyes is something else. Whether he’s in the studio judging beats or onstage listening to his fellow rappers, he has that faraway, genius-at-work distraction in his eyes.

“Fade to Black” is a mostly undistinguished documentary that’s at its best when showcasing this side of Jay-Z. The guy comes across like the Brian Wilson of hip-hop when he’s making a record, combining sounds or channeling lyrics.

The occasion here is a November 2003 Madison Square Garden concert that was supposedly Jay-Z’s showbiz farewell. Like 99 percent of showbiz retirements, it didn’t last, which dims the glitter of this big event.

As we see the concert scenes, the movie flashes back to Jay-Z putting together an album in the studio. This is easily the most interesting stuff in “Fade to Black,” a look at the process of assembling a hip-hop record.

Among Jay-Z’s stops is a session with celebrated producer Rick Rubin, who marvels at Jay-Z’s ability to spray lyrics around without having anything written down. And this is coming from a man with a stuffed bison in his living room.

The concert itself, despite the breathless hype surrounding it, is the usual collection of songs mixed with shots of an adoring, singing-along crowd. Jay-Z gathered a long roster of hip-hop artists around him to fill in the bill, so the show has a parade of people walking on and off stage.

The showstopper, not surprisingly, is Jay-Z gal pal and supernova Beyonce, who appears for a few numbers of her own. The inimitable Ghostface Killah also lends his presence to one of her tunes.

Missy Elliott delivers a boost of energy, and Foxy Brown trots onstage to raise the question of whether she is going to pop out of her bustier. (And this was before Janet Jackson made it fashionable.)

Jay-Z’s best duet comes with Mary J. Blige, who has the pipes to pull the performance in the direction of singing rather than rapping. Jay-Z is moved to exclaim, “That is so (bleeping) soulful,” not one of his most articulate moments, but heartfelt.

There’s also a duet with R. Kelly, presaging a bust-up between Jay-Z and Kelly when they performed at Madison Square Garden recently and Kelly walked off the stage in mid-concert.

“Fade to Black” should have been released earlier this year, before such tomfoolery – and before Jay-Z made it clear that his retirement announcement was premature. Now, the emotion of that proclamation makes the movie seem a little silly.