As for the shell script issue with ffmpeg, this just came up in another thread, where it's really tricky to get the quotes correct when passing things in a var to ffmpeg due to embedded quotes. See @Nige_S' workaround in that thread:
(I posted a stupid silly solution which also works, which is to just type the command into Terminal via KM. Not the right way, but I was just trying to find any way to get it working :)).
-rob.