Ok Mr Guilford, I'll create a user.
I'm logged as myself, and yes I have administration permission.
I started kdenlive as "invited" and there was no lag.

Okay, I suggest running Kdenlive as a normal user - KDE applications are not intended to, nor are they tested for, running as the root user.

Okay thank you for the discussion. I learned a lot.
yours,
Raphael

Hello again, I've been chatting with some people about the situation of my kdenlive usage, and it appears you don't know that I've been obliged to run kdenlive as root user in order to have permission to create a render... I created a new user, and tried to move my whole project in its directory (which obliged me to define new permissions) but this problem of being able to render the files remains...

raphaelpoli wrote:Hello again, I've been chatting with some people about the situation of my kdenlive usage, and it appears you don't know that I've been obliged to run kdenlive as root user in order to have permission to create a render... I created a new user, and tried to move my whole project in its directory (which obliged me to define new permissions) but this problem of being able to render the files remains...

You don't need 'root' or 'sudo' access in order to render a file. You need to have your Linux system reconfigured so that regular users have proper access to any needed resources (i.e. filesystem etc.)

Can you please provide the specific error messages you get when attempting to render a file so we can provide guidance on any additional rights you need to grant?

Well I must apologise, for the error I experienced did not reproduce.
Now the only permission I miss is the one to "create the project folder" at the beggining of the session, but it does not prevent the work.
Thank you for your presence.