I'm trying to record video from a firefox run by xvfb-run but it always output nothing in the video file except black screen. Here's what I did: start a firefox, open google.com: $ xvfb-run firefox https://google.com Then it will use the default display server number 99. I can see the display information by command xdpyinfo -display :99. A screenshot works very well by command: $ xwd -root -silent -display :99.0 | xwdtopnm |pnmtojpeg > screen.jpg Start using ffmpeg to record a video: $ ffmpeg -f x11grab -i :99.0 out.mpg When I play the video file out.mpg, there's black screen all the time. Is there any parameter I missed? Updates I made progress that the video works instead of black screen only by this command: $ ffmpeg -y -r 30 -g 300 -f x11grab -s 1024x768 -i :99 -vcodec qtrle out.mov Notice it requires the screen resolution matches by specify more options to xvfb-run: $ xvfb-run -s "-screen 0 1224x768x16" -a firefox http://google.com But I still want to get more feedbacks and answers here.