A silent film is a film with no synchronized recorded sound, especially with no spoken dialogue. The silent film era lasted from 1894 to 1929. In silent films for entertainment, the dialogue is transmitted through muted gestures, mime and title cards which contain 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 only made practical in the late 1920s with the perfection of the Audion amplifier tube and the introduction of the Vitaphone system. During silent films, a pianist, theatre 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.