Lip syncing is used almost always when a music video features an element of performance. The term (short for lip synchronisation) refers to the matching of pre-recorded vocals to lip movements, in this case on film.
Performing/recording a lip sync
Multiple sources have al insisted on there being two main, essential factors to a successful lip sync: rehearsal and editing. Firstly, the song should be properly rehearsed by the vocalist, ensuring they know exactly when each beat/lyric occurs. Then, start playing the music aloud 10 seconds before the shot actually required; this ensures the vocalist is in time. Also, it is absolutely necessary that the artist is singing out loud meaning their breathing, shoulder movement and facial expressions are real and thus are more believable, improving the quality of the lip sync. Finally, each shot should have multiple takes that enables you to pick footage in which the vocalist is in sync properly.
Moreover, if the budget allows for it, directors may choose to use 2 cameras to film lip-syncing in order to cover more angles. When two cameras are being used, one is often mounted on a tripod, dolly or crane etcetera and the other hand held (as seen below)
However, if the singer is directly addressing the camera, then only 1 is used to avoid any confusion.
Current uses of lip-syncing
In almost every music video, lip-syncing will occur at some point, if not consistently throughout. This allows the audience to see the song associated with the artist more frequently – this can then increase the fame of the artist and help sell more copies – so it is no surprise that music labels include lip-sync so frequently.
In 2015, a new television program was premiered based on the concept of lip syncing. Lip Sync Battle involves celebrities competing against each other through lip syncing (or miming) to a song. This new direction for lip syncing is bound to alter the way audiences perceive it by making them more conscious of the fact the ‘singer’ is not actually making the sound you are hearing. This could mean that the audio and video will have to be ever more synchronised.
Below is the link to a thread with various tips on lip syncing in Music Videos: