Fails on Ubuntu 18.04.5 LTS

[skanga]

$ xhost +
access control disabled, clients can connect from any host

$ ffscreencast
/usr/bin/ffmpeg -hide_banner -loglevel info -thread_queue_size 512 -f x11grab -video_size 1280x720 -i ":0.0" -c:v libx264 -crf 0 -preset ultrafast -threads 0 "/home/skanga/Desktop/Screencast 2021-01-24 at 13.26.31.mkv"
Invalid MIT-MAGIC-COOKIE-1 key[x11grab @ 0x5571a21139a0] Cannot open display :0.0, error 1.
:0.0: Input/output error

[Manas Singh]

echo $DISPLAY will give you :1 but ffmpeg is using -i "0:0" is the problem.