x11grabr and ffmpeg

# x11grabr is from here https://github.com/livibetter/x11grabr

# works fine
./x11grabr -s 1920x1080 -r 25 -bnone | ffmpeg -f rawvideo -pix_fmt bgra -s 1920x1080 -r 25 -i - -y -r 25 test.mp4

# seems to work fine but the duration of the mp4 file is wrong
./x11grabr -s 1920x1080 -r 25 -bnone > tmp
cat tmp | ffmpeg -f rawvideo -pix_fmt bgra -s 1920x1080 -r 25 -i - -y -r 25 test.mp4