how to use video_upload_default_path

First thanks for all your work on this stuff - great job !

I'm looking all around and do not find an answer to this question.
I would like to create an upload folder per user for video. Looking at the module code I can see that variable video_upload_default_path is read from init but I do not know (or understand) how to set it. My purpose is to manage easily what user needs to push to the server and do not overlap with others. In fact I also want to have a different upload folder than for images. By default video_upload use upload definition and add video directory behind, but I would like to have it at another location.
I have taken a look and I think we can declare this variable in variable table but I do not understand the syntax

Here is what I have
/files <--- upload module
/files/images <--- image
/files/videos <--- video module

Here is what I would like:
/files <--- upload module
/files/images <--- image
/media/videos <--- video module
/media/videos/user1 <--- video repository for user = user1
/media/videos/user2 <--- video repository for user = user2
/media/videos/user3 <--- video repository for user = user3
...

Any idea on how to do it?

Thanks