Hi Renato !
I didn't do the now quite famous "Les Ramens" video, if you were speaking about that one, but I can explain you the trick to do a proper video recording of the looper ^^.
The key is to have an headphone splitter that you plug on your output jack. That way you then have 2 jack outputs. Use one of these to plug-in your headphones as usual, for monitoring purposes, and use the other one for recording the looper output.
If your camera has a standard line input (probably 3.5 female jack), then you can plug this extra looper output directly there with a 2 sided 3.5 male jack cable. Activate the "Microphone PassThrough" option and both your live sound and played loop will be heard and recorded.
If your camera has not that, you will have to record the sound on your PC (same method as above, but the PC replace the cam), and then do some editing to stick video and sound together.
Hope I've been clear enough

!
Have fun and keep us updated if you release some videos !
Raphaël