ROFLMAO right now. Funniest youtube vid I’ve seen in awhile. Always loved this Gatlin Brothers song.
How did he do it? 
He’s got the trucks bouncing in time to the beat and put mouths on them. The mouth seems pretty straight forward. The six trucks bouncing in perfect time has me astonished. They are moving in different ways. 
A “warp” tool with animated keyframes. I don’t know what program this person used, but Photoshop has a warp tool that can do it. One of the top of each truck, from the top of the mouth to the top of the truck, another for the bottom of the mouth to the ground. Smaller ones for the headlights. Put the teeth into a lower layer to be revealed as the warps move the lips.
It looks like he just animated the teeth and ‘moved’ the truck fenders/grills to match the mouth movements. If you look under the trucks you can see the road moving as well where he cut it out a bit too much (or maybe he needed to to that so it wouldn’t look choppy, I’m not sure.
It’s a clever idea. I like how when there’s a solo voice the other trucks keep moving to the beat.
Fan vids are making such clever stuff these days.
Animating the mouths would take longest, but he’d only need to do it once then apply it to the other trucks with only subtle changes. But that’s the last step (apart from the clunky camera zoom).
The first step* was animating the bounce of each truck, which he may have recorded in real time (judging by the naturalistic bounce), by simply bobbing the main control as the song played, and the clever warp grid he set up made the trucks move in a reasonable facsimile of 3D with no extra effort.
*Actually, the headlight blinks may have been first
You would probably want to do everything that stays in place before having it start to move.
So he took a still photo of the trucks and warped the mouths a little, then saved it as the first frame of the video, warped them a little more and saved it as the second frame, and so on?
Adobe After Effects is great for manipulating video. But its extremely expensive and not something a home consumer would have. After Effects integrates well with Photoshop. It can read and manipulate layers in a image. etc.
I used it in a college class that I took. One of the projects was blurring a license plate. (something done in a lot of news video) We selected that area, then created a tracking path as the car drove through the video. Then applied a blur effect.
I’m not aware of any music effects. Bouncing a graphics object in time to a beat. But we only did a handful of projects in that class.
He probably didn’t do it one frame at a time. He could have, of course (that’s the way all animation used to be done), but it’s easier to do it automatically.
And the bouncing is just another warp, not actual video. The original image was completely still, as evidenced by the frozen human in the background.
I’ve done lip-synching in Flash before, and it involves a looooot of setup. This guy probably made images of the front of each truck, then divided them into individual sections like the grill, headlights, bumper, etc. He also incorporated the black inner mouths with teeth for each truck just behind these sections.
He then made key frames (the beginning and end frames of a single animation segment) for every possible sound. The truck mouths widen for EEE, make round shapes for O, have the tongue protrude for T, etc. The key frames for “gold” would be a slight opening between the teeth with a lip pucker for G, the open mouth shape for O, and the slight tongue protrusion for D. He then would have created a morph for the first keyframe into the second, the second into the third, and then sped up or slowed down each morph segment depending on how the particular word is sung. That would have involved a LOT of trial and error, and he did it for 5 trucks!
In addition to the mouth movements, he also has the heads bounce along with the beat, headlight eyes blinking, and other little nudges and facial gestures we take for granted. Animators study the way people move, even the little gestures. Every type of motion a person makes has its own style and flair, and he captured that beautifully. As somebody pointed out earlier, he was a little lazy with the truck on the right, having its shadow warp along with the undercarriage instead of separating the two, but I think that can be excused.
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