Hi @Bruno1,
The sudo apt-get install gstreamer1.0-plugins-good command needs to be run in the terminal over browser window, not in the gstreamer options. I’d suggest you press the “Default gstreamer options” button to restore them to normal, and then go back to your terminal window. If the terminal is still in the video screen session then you can press CTRL+a then d to ‘detach’ from it, before typing in the installer command. It will only work if your companion is connected to the internet.
From there I’d suggest restarting your companion computer, and if that doesn’t work then you likely need to re-flash it.
it’s ok after flash …