fade-in 
noun
A film-making and broadcasting technique whereby an image is made to appear gradually or the volume of sound is gradually increased from zero: the film begins with a fade-in to an exterior scene...
- The four words in Spanish appear down the centre of the image, on a rapid fade-in, dividing the two figures in the frame.
- The words were spilled across the screen in a fade-in and fade-out motif as the announcer spoke them.
- The excerpts taken from complete recordings required some fade-ins and fade-outs, and Decca's engineers have handled these as unobtrusively as possible.