Having been frustrated with the AppleTV in my last post, I have got a workaround which seems to do the job for me.
In iTunes preferences, click on the advanced tab. At the bottom of the first section is the checkbox to “Copy files to the iTunes folder when adding to library”. Unchecking this box allowed me to add the videos stored on my external hard drive into iTunes, without overloading my laptop. From there they then synced over to the AppleTV, and seem to stay there even when the hard drive is disconnected from my laptop.
Okay, I’ll admit it’s hardly ideal! I am hoping that by using appropriate commands I won’t get files littering my hard drive, but at least it makes the AppleTV useful!