system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The slow motion effect in videos, but in real time

Ever seen a music video where the singer is singing along with the real-time track, but it looks like it's all in slow motion? ELI5.
gpt
The music track is played at double speed, and the singer/band practices lip syncing to the faster speed. 

While filming, you shoot at a higher frame per second, and have everyone lip sync to the fast music track.

Finally, you play back the film at normal speed, so everything looks slow motion. But the music was fast, so it's now normal.