Playing (or miming) your instrument in front of a camera for a movie or TV show is called sideline work. Producers sometimes call Local 802 to hire musicians for these kinds of jobs, and the union keeps a photo file of interested and available members.

Ever see a scene in a movie where music is being played? Have you wondered whether that’s an actor or a musician? More often than not, you’re seeing a trained, professional musician, who is being hired to do something that’s a cross between music and acting. It’s called sideline work.

Sideline musicians play – or pretend to play – their instruments in front of a camera, for movies, TV shows or commercials. Sometimes there is a pre-recorded track playing in the background that musicians play along with, or sometimes there is no music at all.

Sometimes sideline musicians are used as technical consultants. The director will be filming a wedding or funeral scene and want to know what kind of music should be used. Or sideline musicians may be asked basic questions, such as “What is a viola?” or “Does a string quartet have a double bass?” The director may decide that in this movie, his string quartet has a violin, two cellos – and a double bass. The director may ask you to provide music for that kind of “string quartet” and not understand why Mozart didn’t write any music for that orchestration.

Sideline musicians are often asked to begin a piece and then fade out until there is no volume at all so that the actors’ dialogue can be recorded. In that case, you have to convincingly “play” without making a sound – even the smallest sound on your instrument would interfere with the sound engineer’s efforts to record dialogue.

The mood and tempo set by the first few seconds of playing is incredibly useful to every actor on the set in how they choose to move through the scene, say sideline musicians. The music is an extremely significant part of the production. At the same time, sideline musicians are often not given any comments on their performance unless there are changes to be made. Basically, no news is good news. (You have to be O.K. with not getting positive feedback – or any feedback at all.)

Sideline musicians may be asked to fake an instrument that they really don’t play well. You could be a flutist and have to fake playing an alto sax. You could be filmed in orchestra scenes behind actors or musicians who can’t really play their “instruments.” Basically, what’s most important in a scene is the actors, not the authenticity of the orchestra or the musicians.

Sometimes you might be asked to play 16 bars of a piece over and over, and never get to the 17th bar.

You may be asked to do a scene as a strolling musician, pretending to play, while the music you’ve been given to fake to is actually a cadenza or something very uptempo. In other words, you might be asked to stroll, smile and play a section that is impossible to play while walking. Sideline musicians say the solution is to do your best, make decisions that are not musically correct, somehow preserve your musical integrity – and look good doing it.

A normal filming day is generally around 12 hours. (But a day could be as long as 15 hours, or as short as four.) You are there until they release you. You cannot leave for a couple of hours to go to a gig, even though some of the time you may just be sitting around doing nothing. Never try to book another gig the same day as a sideline date.

You might be asked to wear clothes that are not comfortable, or you may be asked to bring your own clothes.

You might shoot scenes that take place in spring when it’s actually January. (Rule of thumb: use an instrument that is not your primary one in case the weather is bad.)

You might be asked to play music that is entirely different from the music on the music stand. Or you might be asked to fake one piece while a different piece is playing in the background.

How do you get a gig doing sideline work? The same way you get any other gig in New York City or anywhere else in the world: networking, making connections and getting your name out there. That said, Local 802 does have a referral service, and from time to time movie and TV producers call the union looking for musicians for sideline work. For more information about 802’s referral service and how to send Local 802 your photo, call Julie Ferrara, the coordinator of the referral service, at (212) 245-4802, ext. 156 or e-mail Referral@Local802afm.org.

Speaking of photos, how important are looks in sideline work? You don’t have to look like a supermodel, but you do have to have self-confidence in your own appearance. Directors can sense your self-confidence: it’s what sells you.