Why Super slow motion video quality sometime seems poor in S9|S9+?

Super slow motion captures 960 frames per second so needs sufficient light to show clear video compared with normal video at 30fps and low motion video at 240fps. If you record a super slow motion video in dark areas noise may occurs.

It means Super Slow motion use very fast shutter speed. In comparison with normal video, Super slow motion use short exposure time and high sensitivity in the same illumination.

Streaks on Super slow motion video are caused by flicker of light source. As Super slow motion use very fast shutter speed, a flash of light that is invisible to the human being is recorded on the camera. And it appears shape of line in the characteristics of the camera(CMOS) sensor.

When using Super slow motion under a flash light source, line appears differently according to shooting direction of camera. For example when you placed the phone vertically, flashing line appears vertically.

In case bandwidth of line, it is influenced by the flicker frequency of the light source. Usual light source flashes at 120Hz and there are various light source with different frequency. In this case bandwidth of streaks is shown differently. 

Thus please record a Super slow motion video in a place that has sufficient light.