Why is there a green dot moving in the video?

Because strong light will produce glare, commonly known as "ghost".

It usually appears in photos, especially when shooting against the light. We call this phenomenon of whitening and halo caused by strong light "glare".

When sunlight or a point light source enters the lens, after many reflections, a clear bright spot is formed at the relative position of the light source, just like a ghost, which is called a ghost. A ghost is a kind of light.

Method of avoiding ghosts: Try to avoid taking photos against the light during the day and try not to let unnecessary light sources appear in the scenery at night.

In addition to the shooting method, the equipment itself is also one of the main causes of stray light. Theoretically speaking, the more complex the structure of the camera lens group, the more stray light.

Because the complex structure means that there will be more unnecessary reflection and refraction inside. For mobile phones, lens protective film and external lens are devices to increase the structural complexity of camera "lens group".

Fingerprints or stains or even scratches appear on the lens. These will obviously strengthen the role of stray light, especially make glare more obvious. If sometimes the photos taken are strange, maybe it is better to wipe the lens.