@Cecilia

How did you make it?
I would really like to produce something like this, but with a much slower pace.

For my first video rendering with YafaRay, I chose a sunlight simulation.
In order to reduce the rendering time in SH3D, I used a speed of 2x with a frame rate of 25. Then I doubled the duration of the video in an editor.
The more recorded positions you have, the slower your animation will be.

My last video rendered for five days – before it crashed and left me with nothing.
That was not the first time I had a crash during video rendering – in fact, ALL my video renderings have crashed at some point – leaving me with nothing.

Video crashes only happen with the SunFlow rendering engine? It seems that your old bug doesn't happen with YafaRay.

Is there any possibility that an unfinished video can be saved, like it is for an unfinished rendering?

To make an animation, Sweet Home 3D assembles JPEG images into a Quicktime video.
The JPEGImagesToVideo class does not allow to recover the part of the animation which has already been rendered.
Unfortunately, an interrupted video is not playable.

Enko