One of the best things about “A Late Quartet” is that director Yaron Zilberman (and his cinematographers and audio engineers) makes the audience believe that actors Christopher Walken, Philip Seymour Hoffman, Catherine Keener and Mark Ivanir are seasoned professional musicians.

Yet it’s the Brentano Quartet gloriously playing the piece referenced in the  film’s title: Beethoven’s String Quartet No. 14 in C Minor, Op. 131, an apex of chamber music written just a year before the composer’s death.

Although music is central, the movie is really a “show must go on” backstage drama, set in concert halls and rehearsal rooms.

Ivanir — an Israeli actor and, of the leads, the least known to American audiences — is outstanding.

He plays first violinist Daniel, who is tutoring and having an affair with Alexandra (a lively Imogen Poots), the daughter of second violinist Robert (Hoffman) and violist Juliette (Keener), whose marriage is falling apart.

Walken is a large presence as Peter, cellist and founder of the 20-year-old ensemble, who is diagnosed with Parkinson’s disease just as the group starts preparing for an important anniversary performance of the Beethoven work.

Life, agony and music unfold in Manhattan, leading to a climax that has musical and dramatic impact, even though many of the central characters’ conflicts do not get resolved.

“A Late Quartet” is attractive, impressive and of special interest to music aficionados. The movie’s impact, however, is diminished by a constant accumulation of relationship problems that make it more melodramatic than the director might have intended.