Hi @AkosFarago ...
I tried viewing the same 8-second video that I had embedded on a new page (described above) with your patch in place. However, even though the annotation icon does show up now (see screenshot), when I hit the play button to watch the video, the timeline completely ignored the annotation like it wasn't even there.

I even tried clicking on the annotation icon several times (while the video was stopped and while it was playing), and it would not show the annotation that I had created.
Then, I tried clicking on the "Studio" icon in the global navigation menu, and then I created a quiz on this video with a True/False question. The True/False question was put a couple seconds after the annotation. (I also told it I wanted to show annotations, too.) After I built the question, I went back to my course and re-embedded the video on the page so that it would use the quiz. When I tested out the video this time, the video did stop on the annotation so I could see it. However, I had to click on the "Continue" button several times (at least four or five times) in order to make the annotation disappear. Each time I clicked on "Continue", it was like a quick flicker of the screen on the video...showing the video for a quick fraction of a second but then returning to the annotation. Once the annotation went away, then it stopped on the quiz question.
Also, if I were to place the cursor back on the timeline of the video near the start of the video and play it again, it skips over the annotation and only stops on the quiz question.
So, it seems like there are some bugs yet that need to be addressed...at least from my perspective.
Thanks....