[Davy Gunarso] "video moving slower than normally and sometimes with a few breaks for each second. I wonder why?"
read this:
https://forums.adobe.com/thread/684381
seems you are a beginner in this software. this is not a software you can intuitively go about and understand how it works, for training start here:
https://helpx.adobe.com/uk/after-effects/tutorials.html
Roei Tzoref
2D/VFX Generalist & Instructor
♫ AeBlues Tutorials ♫
http://www.tzoref.com 
