With video, it is quite difficult, as you need to know when the video file writing stop. I found out that a lot of temporary file writing happen. Probably the best way to do it is to keep a list of file with its datetime. Then sync only the change, probably periodically or on manual trigger basis.
You can also use trigger App Task ended, to detect when the camera app has been closed, wait for certain time. List all the file in the phone and FTP server. Use removeAllElements to remove all existing files in the FTP, so only leaving the new videos which haven't been synced yet. Upload only those unsynced videos.
Trigger File Observer with so many events ticked, can freeze Automagic; especially when you have abused using your glovar lavishly, as I used to do in the past. I will prefer to use other trigger when possible, or only activate the flow for certain period/condition. Check the similar thread for Trigger File observer :
viewtopic.php?f=5&t=6937