Disclaimer: I don't own an android mobile, but would definitely get one if the below were possible.
On my mac, I can use software like CamTwist and SoundSiphon to create 'fake' webcam and microphone inputs.
CamTwist lets me pipe custom content (such as images or video) to that webcamera input, and SoundSiphon makes it easy to have system audio interpreted as microphone input.
Q. Is it possible to achieve something similar to the above, but on any Android handheld?
E.g. I'd like to be able to use a native Android app (such as Skype or Periscope) and pipe custom video to it (rather than using the in-built camera), whilst simultaneously broadcasting a custom audio file (rather than the in-built microphone)