My car is having problem starting the engine some times.

I turn the key all the way to ignition, it will turn on eventually but it has this jittering 2~3 out of 5 times (I don't know exactly how to explain in words - when engine is about to start it sounds like it's going to shut off but then it gets back on and starts). I'm not sure if it's anything related to spark plug, because I replaced it few months back. I also replaced my battery 6 months ago.. I'm not sure what could cause this.

Anyone has this problem?

 

maybe the starter going bad