I know besides the URL tag there is the IMG. But how to combine them I don't know.

i assume you mean posts on this forum.
you can't even post normal images on this subforum, let alone videos.
if it was allowed, i would do the following:
[url="YOUTUBE URL"][img]http://site.com/imagefile.ext[/img][/url]

some forum softwares allow video embedding, iirc on one of them the tag was
[embed]YOUTUBE URL[/embed]

The must be something wrong. I am watching the youtube video, I press ^L copy and paste the URL in the URL bar. And this is the only URL that matters. But according to your syntax there are two URLs!

Members cannot embed videos in posts.

--jeremy

Is this a machine I am taking with? I think you should carefully read the post.

LOL, stf, you've been a member since 2007 and you do not know who Jeremy is?

YouTube will hand you the HTML needed to embed their videos. Whether or not this will work in a forum post depends on the forum.

And, generally speaking, if you have a video you want me to see, I want to see its URL, so that I can choose(!) whether to watch it.

You don't (cf #4).

agreed.

what i posted previously is a visually more appealing option that does not embed anything and should work on most forums that support images.
nota bene, not all of LQ's subforums support images.

Let's put a concrete case. This is the URL I got by copying the URL box contents (screen upper side) while watching the video. I know youtube can give you the video URL after you performing I dono what action but lets forget about that:

https://www dot youtube dot com/watch?v=8_7xer_O1rA

In the particular forum I want to post, ]URL[]IMG[https://www dot youtube dot com/watch?v=8_7xer_O1rA]IMG[]URL[ (square brackets the other way round intentionally) is what I put. But without a result. The problem is different forums have different formats, I think. For instance in the beethoven reference site, which is where I did the test, only a part of the string is enough. So?

This has been answered many times:

You can't.

Can you be a bit more explicit? I can't what?

You can't post a video such that it's playable in an LQ post.

And who said I want to?

I thought you did, when titling this thread:

If you wanted something else, why don't you just say what it is that you want?