DISPLAY=:1 will select the second X11 display server, which most likely does not exist.
DISPLAY=:0.1 will select the second “screen” of the first X11 display server. Each screen is an independent root window. In real life, X11 servers only ever have on screen (number 0) and multiple view ports are managed with RandR. So also unsurprising that it does not work.
–qt-fullscreen-screennumber=1 should select the second RandR viewport if the VLC Qt GUI and normal/default embedded video playback is in use. That would be the default with upstream VLC and most Linux distros.
However, since you mention an option “–drm-vout-display” that does not and never has existed as a VLC option, I guess that you are using the Raspbian fork of VLC. So then, the Qt option will indeed probably not work. We can only advise to use upstream VLC (or plain Debian/Ubuntu). Otherwise please seek support from Raspbian.
Statistics: Posted by Rémi Denis-Courmont — 07 Jul 2024 08:30