Did you realise that to sync the singer’s lips in a slow motion music video (Take Hymn for the Weekend by Coldplay for instance) is not so trivial.
During the shooting, the song has to played in faster than actuality to assist the singer in lip sync!
In other words, if one wants to make a slow motion video for a song, the audio must be at the same tempo, but the video is on a different “tempo“. This must be compensated! So, if I want the song video to be going at a rate of 0.75x, while shooting, the singer has to sing the same song at 1/0.75x or 1.33x.
Similar idea goes to music videos where the video is played faster than the song (Friday by Rebecca Black… er… rofl… no? haha). No hate please. She’s already had a hard time making the video probably!