The Nixu Challenge 2020 - 3dprint
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Started this one by downloading the mp4 file and watching it. The noise was "quite" irritating, but pretty soon it was obvious, that you can hear which way the printer's moving by the sound.

So now I knew the logic, but it would've been too easy to solve by just watching the printhead move, so the camera was turned away and the sound faded a bit.

As I'm no expert with audio to visualize the sound, I extracted the sound track to .mp3 with VLC.

Next I opened the audio extract with Audacity, enabled Spectrogram and zoomed to see better the approximately correct frequency range for the printhead movement sounds.

The range was about 1020 - 1460Hz and using linear range with Blackman-Harris window type as spectrogram I was able to "visualize" the sounds.

Unfortunately Audacity is missing the option to extract the spectrogram (it was quite wide), so I just used the snipping tool to extract spectrogram in multiple parts.

Next I compared the visualization with the beginning of the video from where you could determine which frequency represented which movement.

Now I just converted the extracted images to black and white, then typed the movements in Pinta to every image.

Example image: 


The last step was to write down all the directions from the images:

_                                 _        _       _           _
_|          _|         |_        |_|      |_      |_     |    |_
_|         |_|    _    |_|       | |       _|     |_     |    |_|

LRULRULR  UDLURU  LR  ULRDLUU  UUDLDUUR  LRULUR  LURLUR  UU  ULRDLUUR
          _           _        _                 _         _      _
    |    |_          |_       | |         |      _|        _|      |
_   |     _|    _     _|      |_|     _   |      _|        _|      |

LR  UU  LRULUR  LR  LRULUR  LUURDDUU  LR  UU  LRULRULR  LRULRULR  UULRU


L=LEFT, R=RIGHT, U=UP, D=DOWN

The sound separting the letters could be seen from the spectrogram too. And the last U is ignored as useless.

The challenge description gives the hint how to spell the flag correctly:
...the flag for you in ba5e16..

So the letters are typed small, even though they seem capital in the decoded message and the beginning of the flag can be seen on the video:
NIXU{3d_ba5e16_15_50_1337} <- can't hear the closing curly bracket either, but logically belongs there.