I discovered blurry parallel rolling dark waves and blurry lower corners my Spark videos. Does somebody know the reason for it?

Please show an example.

Sorry, my fault. It only appears on the iPhone in the preview mode before downloading from the SD-Card.

Can you make a video from the iPhone screen?

This is likely because you watch the video feed that is wirelessly transmitted to your phone. The high compression used creates lots of artifacts. Extract the video from your microSD card instead as this is the "real" one capture by the Spark.

The original videos from the SD card are much better than the cached video and the video view.