Have you tried #OliveNLA?
I've recently switched to it from Kdenlive. However - I hope Kdenlive will step up it's game. It's hard though though when there's thread-unsafe effects in the ppelinie - forcing single-thread rendering. I'm not sure how they can work this around.
@a1batross @kde Than Olive might serve you well. It's still in early stages, but it's ultrafast and surprisingly stable for alpha software. Actually it crashes less than Kdenlive from my experience. The key factor is - Olive does all compositing and image manipulation via GLSL - which is nearly real-time fast in most cases. I was absolutely shocked when I tired it out.
Welcome to your niu world ! We are a cute and loving international community Ｏ(≧▽≦)Ｏ !