You don't need a doorbell camera, get a regular camera instead.
You need an app which will receive events from a doorbell via a server to receive data to interface with the app. Both of those things need to be owned and operated by someone to be approved for use on the app store. That's why a custom open source of doorbell as you envision it doesn't exist and never will.
Btw videos not working well because of absense of hardware decoding codecs, and it is make software decoding.