SMPTE (Society of Motion Picture and Television Engineers) time code is a means of physically addressing points on your recording media by recording unique information showing the hours, minutes, seconds and video frames at any given point on the tape or digital media file. Professional audio and video recording equipment allows you output and input time code from one device to another. When you use a specific device as the time code “master,” you can feed that device’s time code to all other recording media so each shows exactly the same time code. When you cue up an audio source that was fed the common time code, you need only match your audio time code to the video time code, and you know you have exact, frame-accurate synchronization between the two sources.
Professional equipment that features SMPTE time code can be expensive. If equipment with external time code inputs and outputs is not available to you, the next best solution to sync audio and video is to use a clapboard. This tool is frequently found on film sets and serves to provide an exact reference showing a visual sync point to the camera while also recording an audio cue at precisely the same time. As the hinged portion of the board comes together, it makes a “clap” sound. When recorded on both audio and video, you can cue your video to the point you visually see the board come together, then cue the audio to the onset of the clap sound. When these two points coincide, you have achieved perfect synchronization between audio and video.
Maybe you didn’t think of how you were going to sync the audio with the video until after you finished shooting your scenes. The final best method of achieving sync between audio and video is to look for visual cues that would trigger a distinctive audio event. For example, syncing lips to the spoken words can be achieved by finding a “p” sound in the subject’s speech. Making the “p” sound requires pursing the lips together. The act of the lips forming the “p” sound is visually discernable enough to that it provides a definitive cue for both audio and video. Assuming the “p” sound is infrequent, you can use this point to find sync. Other action can be equally useful. There may be natural “clapboards” like a door being closed. Any action that provides a sharp visual and audio cue will provide a suitable point for achieving sync.