Technical question about slow-mo filmed voice synchs

[Will__]

In music videos, when the scene is in slow-motion, as many are, how do they maintain the mouth movement synch to the vocals?
If I had to guess, never having seen how it's done, I'd say they would first speed up the audio track by the same value as the slow-mo video is planned (ie if the slow mo is planned for 66% of normal speed, they would resample the audio to be 133% of normal speed. I'm useless at maths so this second percentage is probably wrong - what's the right one?)
This real-time mouth movement on video, (mouthed too fast in real time as the sped-up audio is played while filming), when slowed down would thus match the normal speed vocal track.
Or maybe I should just get out more?
This question came to me while watching Gwen Stefani in her new cover of Talk Talk's 'It's My Life' which actually has really grown on me. Although I can't say that I spent the whole of the video watching her mouth./
On a separate but related note, I presume that when filming reverse motion music videos, the actor/singer simply has to learn the entire mouth movement backwards? That might be a little obvious but since I imagine it's near impossible to do for more than a few seconds at a time, I thought they might have a technical trick or workaround. And I seem to remember a Coldplay video shown entirely in reverse motion involving Chris Martin in a car crash but I can't remember if it's several long takes or chopped up so he can learn the mouth movements.
Hmph. Longest post here for me!
cheers

[bigred]

Right on both counts. They're both very difficult to do and require a lot of work on the artist's behalf. Classic examples of these techniques are 'No Surprises' by Radiohead for the speed up (the bit in the middle where Thom gets submerged - get hold of a copy of 'meeting people is easy' to see how it's done) and the Pharcyde's 'Drop' for the backwards thing (it's on the 'Work of Spike Jonze' DVD and is an absolute masterpiece). Hope this helps...

[Will__]

cool. Thanks for your reply.

[stoory]

bigred is spot on. artists really need to be perfectly on the beat with the lyrics as it shows more-so than normal when slowed down to 'regular' audio speed.