Below are resolved issues using Yad on Debian based linux with gtk / gnome (Ubuntu) desktops
===NO VIDEO===
Issue # 1 - yad --html --browser --uri="/path/video.mp4" # Plays audio only and video is not shown.
Resolution: Install sudo apt-get install gstreamer1.0-libav first and then remaining in order shown and check issue is fixed after installing each file in order shown.