Unfortunately is seems that Roman Arutyunyan has not been able (or willing) to keep up the development of nginx-rtmp-module. Thankfully, Mr. Sergey Dryabzhinsky has a fork [0] that has added a lot of nice new features (EXT-X-PROGRAM-DATE-TIME!) and some bug fixes.
Lots of good times with ffserver although thankfully https://github.com/arut/nginx-rtmp-module seems to meet the same use cases and exec ffmpeg under the hood.