Home Sharing Movies vs apps like Air Video

I have iTunes running on my iMac with and Apple TV and an Apple router. iTunes library is on an external hard drive. Apple TV works flawlessly.

Given that, I cannot figure out why Home Sharing is SO SLOW. When I try to access my movies and shows on the Video app from my iPhone or iPad, it takes FOREVER for the Shared library to come up, IF at all. Usually it gives an error after about ten minutes of trying. But here's the part that confuses me. If I use my third party app, Air Video, with my iMac acting as the server, I have ZERO issues. The library pops up immediately, and I can watch movies and shows flawlessly. This is the case whether I am at home on my WiFi, or anywhere else. I can be traveling 4 hours away, on Cellular Data, and I can watch my movies instantly. It doesn't make sense why I have so much trouble using Home Sharing when I am at home on the same network. Can anyone explain this please??