A networking protocol is classic erlang/BEAM territory 
That would be done with gen_fsm and records. Structs are definitely the more elixir way to do it. It might be worthwhile to look at gen_fsm for you. I know there’s some efforts underway to write a new implementation in OTP, mostly because the existing one is skewed toward networking protocols, but that’s not really a problem in your case.
Helper functions in the module that defines the struct is great in general but “handle” seems a bit too coarse grained. That probably belongs in the gen* server that manages the specific connection. Yeah, back to the original question, that’ll mean a lot of pattern matching function heads, but you really do want low processing overhead in RTMP, so that’s my recommendation.
