Silent film is a film with no synchronized recorded sound, especially with no spoken dialogue. In silent films for entertainment, the dialogue is transmitted through muted gestures, mime and title cards with a written indication of the plot or key dialogue. The idea of combining motion pictures with recorded sound is nearly as old as film itself, but because of the technical challenges involved, synchronized dialogue was made practical only in the late 1920s with the perfection of the Audion amplifier tube and the introduction of the Vitaphone system. During the silent film era (from the mid 1890s to the late 1920s), a pianist, theater organist, or, in large cities, even a small orchestra would often play music to accompany the films. Pianists and organists would either play from sheet music or improvise; an orchestra would play from sheet music. The vast majority of the silent films produced in the late 19th and early 20th century no longer exist. A September 2013 report by the United States Library of Congress announced that a total of 70% of American silent feature films are believed to be lost.