I am having the same problem.
I have a massive selection of DVDs which I changed over to APPLE TV mp4 format, put them into my itunes library with all the relevant metadata etc - Album Art etc.
I have no problem seeng everything that is in my library, all correctly filed, movies in movies, TV Shows in TV Shows all broken down.
When I try play them it takes forever - nearly 10 mins to watch anything. As soon as it starts then, it will load the entire 2 gig movie in about 10 seconds direct from my Home Sharing Network.
I have no problme with Music, or Photos, they start straight away.
My movies etc all play perfectly and straight away when using the Home Share on the ipad as well as the iphone - everything show up and works exactly as it should.
The Apple TV 3rd Gen which I got for Christmas is just too slow to load and starting to annoy me.
Please can you help 😟