start engine before client

[Vasilisc]

The program "app1" is not mine. It consists of two parts.

I create snapcraft.yaml
--------------------------------
apps:
  engine:
   command: $SNAP/opt/app1/engine --start
   plugs: [home, unity7, x11, pulseaudio, network, network-bind]

  player:
   command: $SNAP/opt/app1/player "$@"
   plugs: [home, unity7, x11, pulseaudio, network, network-bind]
--------------------------------

If to launch an engine (app1.engine) and then the client (app1.player), 
then everything works perfectly. How to make that start of the client 
automatically launched an engine?

Sorry for my english.
-- 
Best regards,
vasilisc