Thanks. It doesn't play with me either. This post was published on dtube.video. I am testing the site. I'll figure it out how it has to be done :)

The original file which I've uploaded is in mts format. Maybe that's the reason. The second cause could be that I've edited the post here on steemit after it was published on dtube. Now I can only edit it on here (on steemit) and not there.

Eh, I'll learn ... :)