Two WM running on one local machine.

WM - Fluxbox.

Using ffmpeg to record desktop.

ffmpeg -an -f x11grab -s 1920x1080 -r 25 -i :1.0 -sameq /tmp/video.mkv

On one display everything works great, but not when i have another WM display startx -- :1.

What i am doing right now is to switch ctrl+alt+f8 to display:1.0, and start recording with ffmpeg. Everything is fine until i switch back ctrl+alt+f7 to display:0.0, WM and captured video image freezes, but when i switch back ctrl+alt+f8 to display:1.0, it unfreeze and continue recording.

So, how to make display:1.0 not to freeze, while on display:0.0?

Tested some more.

open [display 0.0]
open [display 0.1]
from [display 0.0] = open => [display 0.2] same problem

For different users and same users results are the same. ffmpeg keeps recording that paused image.

Looks like WM root window need to be active, to be recorded.