This happens if you are running a kdenlive script from the shell of a remote machine without using SSH "-X" forwarding and it will also cause any areas where you write text to be a white screen for that duration.
melt FusionFestival.kdenlive
No LADSPA plugins were found!
Check your LADSPA_PATH environment variable.
[producer_xml] failed to load transition "qtblend"
[producer_xml] failed to load transition &q........
#if you have nvidia make sure you install the nvidia-cuda-toolkit so hardware acceleration can be used
wget http://ffmpeg.org/releases/ffmpeg-3.3.2.tar.bz2
tar -jxvf ffmpeg-3.3.2.tar.bz2
cd ffmpeg-3.3.2/
./configure --disable-yasm
install prefix /usr/local
source path ........