Cycles: pixel problems, not on first frame ... How to solve? See here the first rendered image (Cycles engine). You can notice that the background does not look very pixelated at all. This quality is fine:



However, in my renders (same Cycles engine, same render ... just some frames later), in subsequent frames, the background (and everything else) suddenly becomes very pixelated:



I hope this question can be answered. I have not found any other answers on this website, because this question does not relate to fireflies, and the render dimensions stay the change.

@Yohello1's comment -> Here are my output properties:



I render the video via my Mac's terminal:
As @thibsert implied, it seems to be the video-codec which creates the problems. If you change it to e.g. H.264 the problem is solved.