The closest to modern consumers will be incredibly out-of-sync audio and video these days is a poor buffering video stream. Outside streaming video, however, is a rare occurrence digital television and digital projection system in cinemas that ensures that the video and audio are properly synchronized.
Although we simply came across such a quality, films were not always such a miracle of synchronicity. Early innovators in the film area struggled for decades to get synchronized audio to the big screen. The earliest movies with some kind of soundtrack simply played music to accompany the movie without trying to sync the two together. Thomas Edison and William Dickson experimented with a system called the kinetoscope, with small single-view machines and scaling it up to the cinema. The cinema system relied on an elaborate but ineffective mechanical system of pulleys and other devices to maintain the synchronization between the movie and the sound. It failed more than it worked, and it was never fine-tuned enough to allow for a consistent synchronization dialogue.
The innovation process continued, but most of the time the inventors were addicted to trying to synchronize a standalone recording with a standalone movie. While the two may have been created at the same time, they are synchronized consistently after it proves to be almost impossible to recreate with some kind of consistency.
Everything that changed when American inventor Lee De Forest built Finnish research inventor Eric Tigerstedt and German inventors Josef Engl, Hans Vogt and Joseph Massole built a commercially viable camera system that recorded the sound directly on the film that the film itself shot. For the first time in history, you could record both the visual and the auditory components and keep them in perfect synchronicity.
The quality of the recordings was poor overall compared to standalone movie cameras and recorders. Even with improvements, De Forest had trouble signing in to Hollywood with the device, as the studios were highly resistant to changing how they did things and at the expense of retrofitting cinemas for new movie technology. While no full length films were ever shot using the technology, De Forest and his coworkers played dozens of Vaudeville acts, early jazz artists, and even Franklin D. Roosevelt. Entertainment historians are treating De Forest's recordings as they capture many historically significant players in the Vaudeville and Jazz scene that otherwise would never have been recorded in such a way.
Although Phonofilm never became a standard, it influenced the strong industry and the variations in the sound-on-movie system dominated the film industry until the advent of digital projection.
Image ̵1; Public Domain.