By the way, it looks as if the module would not even touch the source code. There is just the link, exactly like I put it. But I got an entry in the log file, which says:
Retrieved embed for: https://www.youtube.com/watch?v=… [page:241698, field:bodytext_ck]
So the module seems to work (I replaced the v= with dots as otherwise the video appears here.) Any idea what might be going wrong?