Adjusting the map ratio in such a way that Time Manager videos are consistent with YouTube resolution formats

I’ve recently made a time lapse video depicting migrants deaths in the Mediterranean Sea and surrounding areas in 2020. It was made in QGIS by means of the Time Manager plugin. I’ve uploaded it here on youtube.

As one can see, the points that represent the fatalities are not circles, but ellipses. This is because the original images that comprised the video had to be adjusted so as to fit the appropriate aspect ratio of YouTube videos, which in this case is 640 x 360 pixels (360p).

However, I’d like to prevent these elongated circles / ellipsoids from being shown in future videos. I want them to be circles.

How do I change the ratio of maps in QGIS in such a way that Time Manager videos are consistent with YouTube’s image resolution formats?