Here is an image of a stamp depicting German composer, conductor, pianist, guitarist and critic Carl Maria Friedrich Ernst von Weber (1786-1826) conducting his Romantic opera Der Freischütz ("The Marksman," 1821), designed by Hölzing, printed by lithography, and issued by Germany on May 13, 1976, Scott No. 1215, Michel No. 894, plus a YouTube link to an excerpt from the Overture to Der Freischütz performed in 2014 by the Berliner Philharmoniker, Myung-Whun Chung (1953- ), conductor.
Here is an image of a stamp featuring a portrait of German composer and theater conductor Carl Emil Paul Lincke (1866-1946), considered the "father" of the Berlin operetta, designed and engraved by Leon Schnell (1888-1961), and issued by Germany (Berlin) on September 3, 1956, Scott No. 9N142, Michel No. 156, plus an image of an autographed photo of Paul Lincke, and a YouTube link to a 1937 recording of German coloratura soprano Erna Sack (1898-1972, known as the "German Nightingale") singing the Glühwürmchen-Idyll ("Glow-worm Idyll") from Paul Lincke's operetta Lysistrata (1902).
Here are images of the three stamps in a set depicting various paintings of Wolfgang Amadeus Mozart (1756-1791), and others, designed and engraved by French artist Eugčne Lacaque (1914-2005), and issued by Monaco on May 4, 1981 to commemorate the 225th anniversary of Mozart's birth, Scott Nos. 1277a, and 1275-77. Bonus: Dog.
"Mozart with his father and sister," by French dramatist, painter, architect, set designer and author Louis Carrogis Carmontelle (1717-1806).
"Portrait of Mozart," by German artist Lorenz Vogel (1846-1902).
"Mozart conducting his Requiem two days before his death," by French artist Francois Charles Baude (1880-1953).
Here is an image of a stamp featuring a portrait of Emmerich Kálmán (1882-1953), a Hungarian composer of operettas, designed by Adalbert Pilch (1917-2004), engraved by Rudolf Toth (1918-2009), and issued by Austria on October 22, 1982 to commemorate the composer's birth centenary, Scott No. 1226, plus an image of a photograph of Emmerich Kálmán, and a YouTube link to a 2013 performance of a duet for soprano and tenor, Komm mit nach Varasdin ("Come with me to Varasdin"), from his operetta Gräfin Mariza ("Countess Mariza," 1924), featuring vocalists Katerina Beranova and Claus Durstewitz, accompanied by the Hungarian Philharmonic Chamber Orchestra, Antal Barnás directing. Bonus: Mask.
Here are images of the two stamps in a set commemorating the centenary of the death of Russian composer Mikhail Ivanovich Glinka (1804-1857), designed by S. Pomanski, printed by lithography, and issued by Russia (USSR) on February 23, 1957, Scott Nos. 1907 & 1908, Zagorski Nos. 1887 & 1888. The first stamp features a portrait of Mikhail Glinka, and the second stamp depicts a scene from his opera "A Life for the Tsar" (1836), a "patriotic-heroic tragic opera" in four acts with an epilogue (during the Soviet era the opera was known under the name "Ivan Susanin"); also I have provided a YouTube link to a recording of the rousing "Glory Chorus" from the epilogue of this opera, performed by the Orchestra and Chorus of the Bolshoi Theatre.
Here is an image of a stamp featuring a portrait of Sorbian composer and conductor Korla Awgust Kocor (1822-1904), designed by Gerhard Wilhelm August Stauf (1924-1996), engraved by Helmut Nebel, and issued by East Germany (DDR) on January 25, 1972 to commemorate the 150th anniversary of the composer's birth, Scott No. 1351, Michel No. 1733, plus an image of a photograph of Korla Awgust Kocor, and a YouTube link to a recording of his musical composition Rjana Lužica ("Beautiful Lusatia"), the Sorbian National Anthem.
Here is an image of a stamp honoring Czech violinist and composer Jan Kubelík (1880-1940), designed by Karel Demel, combined engraved by Martin Srb and photogravure, and issued by Czech Republic on January 19, 1994, Scott No. 2912, plus an image of a photograph of Jan Kubelík, and a YouTube link to a 1913 recording of Kubelík playing Zigeunerweisen ("Gypsy Airs"), Op. 20, a musical composition for violin and orchestra written in 1878 by the Spanish composer Pablo de Sarasate (1844-1908).