When you close the three holes next to the blowing hole, you get the key of the Dizi, which is D in my case as well as in this video, and if I close all the holes, apparently I get an A. In this case, D is "1" in numbered notation and A is 5 with a dot under it, the lowest note in my Dizi:
But the song in the video is in G, and I can't even know what's going on anymore. The music starts with that "5 with a dot under it" but he's playing what is "1" in our Dizi in D (closing the three holes next to the blowing hole).
I didn't study music theory in depth yet. There are many things I don't understand yet. Is that the problem? Is it a transposing instrument or the song is transposed? I'm sorry if my question sounds silly, but my previous plastic flute was in C and now all of a sudden the songs are confusing.
Keep in my that if I follow the standard music notation as it also shows in the video, it works fine and natural. But Chinese music is almost always written in numbered notation. I have to understand what's going on.