YouTube is many things to many people: a place to find old clips of What's My Line, to watch cats do funny things, to see people get their umpteenth tattoo. But increasingly it's become a place that is a repository of classical music and, perhaps important, a tool for current musicians.

Now, for the most part you don't see full-length videos of classical performances here (unlike at this website). You're more likely to find snippets of a singer emoting her way through an aria.

But what a treasure trove. Régine Crespin and Franco Corelli singing "Teco io sto" from Un Ballo in Maschera or Crespin talking about her art. Hildegard Behrens performing arias from Tosca or singing as Senta in Der Fliegende Höllander. Dietrich Fischer-Diskau bringing his interpretive intelligence to Schubert.

Sometimes you get a recording from decades ago and rather than the singer singing a visual montage either of a photograph of the singer or of related art. Callas performing "La Mamma Morta" from Andrea Chenier has images of her face, and those of art depicting the French Revolution.

These are fascinating, and one could browse for hours picking and choosing from a video history of singing of the last century. 

But apart from the fan-fix for diva worshipers, YouTube is serving a real need in a time-pressed, cash-strapped age. Singers can post performances online as a kind of virtual résumé, and save the expense of traveling to auditions until near the end of the process.

I know one opera company's casting consultant who found a Donna Anna for Don Giovanni this way. He and his colleagues referred to the singer as "YouTube Girl" to differentiate her from those who lived closer, but online they had been impressed by her appearance, the way she looked when she sang, so that she was a real contender for the role, more so than if she'd merely sent an MP3 recording of her work. When she showed up for an in-person audition, they were better prepared for the person who walked in than if they only had an idea of her from recordings and photos.

That's the difference. Hearing Callas sing "La Mamma Morta" is great, but you'd really also love to see her facial expressions, her entire body acting the role, to get the full picture of her greatness. Even though YouTube is only an approximation of a full-screen performance or a live one, having the visuals match the vocals, rather than comment on them, is a real plus.  

But it's good to have any classical music videos. Several of the major organizations, such as the Metropolitan Opera and the New York Philharmonic,  have their own YouTube channels, to provide high-quality excerpts. More will follow. Like most online ventures, it will serve as a promotional tool, a reference library and a communications device.

But for full operas and other classical musical performances, you need to look to other sites. Such as this one.