SAN FRANCISCO (AP) - Spotify is about to find out whether investors view its music streaming service as a budding superstar or a flash in the pan.

The Swedish company will make its stock market debut Tuesday, casting a spotlight on its early lead in music streaming. That's a still-evolving field trying to hook people on the idea that it's better to subscribe for online access to millions of tunes than to buy individual albums and singles.

Spotify has struck a chord with 71 million worldwide subscribers so far, nearly twice as many as Apple's music streaming service. But it has never been profitable, raising worries that it will eventually be upstaged by Apple or other powerful rivals.

Optimists contend Spotify could become as successful in music streaming as Netflix is in video streaming.