iOS – higher mobile traffic

iOS: Why is total mobile data traffic slightly higher than video statistics indicate?

Although the movie is not playing and no data should be preloaded, it seems to be going to a little data traffic when a video page appears in my iPhone. Why?
In the Safari browser on iOS devices (iPhone & iPad), it turns out that the iOS operating system still uploads 298 KB of data after all. This can lead to, for example, unexpected costs for those who do not have unlimited transfer volume in their mobile plan.
The problem is brought to the attention of several quarters and is given a detailed explanation in this article: