Got black screen when recording screen from xvfb by ffmpeg x11grab device

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.

Solution 1:

I happened to have the same problem and found out: you have to specify the depth (16 in this case) so ffmpeg won't produce the black screen.

e.g.

Xvnc -geometry 1024x768 -depth 16 :10  <<---WORKS
Xvnc -geometry 1024x768 :10            <<---does NOT work, produce black screen.

Solution 2:

I had the same issue. Seems like it had something to do with the version of ffmpeg available in the official Ubuntu packages (Kubuntu 15.04 in my case to be precise).

I downloaded the ffmpeg sources and with a bit of help of the docs I managed to get something running.

The build process takes a long time! And by default many features (x11grab among others) are disabled. I ended up with the following:

./configure \
    --prefix=/home/exhuma/.local \
    --enable-x11grab \
    --enable-gpl \
    --enable-libx264 \
    --enable-libmp3lame \
    --enable-nonfree

I now have both video and sound.