How to force multithread on video rendering? I use Blender as a video montage software and the issue happens during rendering.

Blender doesn't use all the cores of the machine. In fact it uses only one. However, I set the threads value to fixed 8. 



And I still have a single thread rendering. 



I thought I could find the answer here but obviously it's not the same problem.

The GPU is unemployed too. 

Who knows how to use the whole machine?

Edit: I precise that I use Linux and other softwares work fine with multithreading.
You can use Pulverize to do multi-process rendering from Blender's Video Sequence Editor:

https://github.com/sciactive/pulverize

Pulverize will render multiple parts of your video in separate processes, then concatenate them into one video file using FFMPEG. It uses the Blender command line to select frame ranges for each render.