In the modern world file sharing is becoming more and more popular. For those who aren't familiar with the term file sharing it's the illegal downloading of music, movies, t.v. shows and other media blocked by copyright laws. Sometimes the quality of 'bootleg' movies and t.v. shows are pretty good. Other times the quality is just pitiful. Ever watch a movie where the sound doesn't match up with the movie? well you can blame physics for that one.
When we watch a movie we are simultaneously processing two different waves. Sound waves are being emitted by the speakers while light waves are being emitted by the screen. well what are waves? A wave is a repeated disturbance which carries energy. However, sound is a mechanical wave- it requires a medium to pass through. If you're listening to sound through a speaker then the wave is using air as its medium. But a light wave is an Electromagnetic wave- it doesn't require a medium to pass through. Additionally, a sound wave is a longitudinal wave so the vibrating particles of the wave travel in the same direction as the wave velocity. While light waves are Transverse waves- the vibrating particles travel perpendicular to the wave's velocity. Now that we established that these waves have different characteristic you maybe be able to understand why they travel differently.
At STP a sound wave travels at 331 m/s through air. While as you know light travels a lot faster. In a vacuum it travels
3 x 10^8 m/s. It takes precision to line up the sound and light waves so that they travel at the same velocity to the viewer. When a glitch in the movie occurs a delay in the sound or light waves occurs. If you're lucky they will both glitch at the same time. In this situation you only miss a portion of the movie. But lets suppose it's you're unlucky day and the sound glitches. There is a delay in the sound waves emitted from the speakers but none in the light waves. Therefore the rest of the movie you will see everything before you hear it. Yes. it's that frustrating moment where you can clearly see a persons mouth moving but have to wait 8 seconds to actually hear what they just said. the velocity of sound can only be changed by the type of wave or by the medium. In this situation you there for cannot change either. Unless of course you have mad skills. Ahh yes physics is the karma of illegal file sharing.