I want to create Android application for Camera with chroma video

Question

I want to create an Android application which can shoot video and merge with overlay video which will be having chroma key.

Concept :- Video recording with having overlay video and audio.

I tried to use Surface View/ Texture View and FFMPEG. In which Surface View/ Texture View are failures. FFMPEG is working but there are plenty of drawbacks like,

1. Processing time is very high.
2. Zoom/ PAN features are not satisfying.
3. Zoom in feature us absent.

Can you please suggest something, I know plenty of application doing same but no idea how.

thanks in advance :)