Making a watched folder wait for a file to finish rendering

I'm trying to setup a watched folder (using fswatch)that starts to convert a received file into another format using ffmpeg(got that part sorted out). So far so good, what I'm having problems with is getting the script to wait until the original input (or master file) has finished rendering or has been copied completely into my watched folder.

Here's the script for the folder

fswatch -o ~/Desktop/autom_shell| xargs -n1 ~/Desktop/scripts_autom_shell/ filters and moves quicktime movies from my receiving folder to the folder where I encode.

I've searched for a solution and found kqwait but I have absolutely no idea how to apply it in my case.

MacOS 10.10