Why is the resolution of my clips on Twitch so bad?

I occasionally stream, sometimes with funny as well as cool moments… Since I like to capture those moments, I often create clips myself because I do not have that many viewers who could do that…

Unfortunately, I always make it clear that the resolution of the clips is totally bad and everything is pixelated. Is there a setting I need to change? If yes, which?

A link would be handy