I will use Gumby's post above as an example.
Click the arrow circled in blue.
The youtube clip will change as shown below.
On the circle in Red right click copy all the embedded link and paste it on notepad.
View attachment 28015
On notepad you will get something like this below.
Copy all the characters circled in Red only.
View attachment 28016
Open a new blank notepad and paste the characters you copied above
and place them in between exactly as shown below.
You can then paste these shown below on your post.
View attachment 28017
Thats it.
make sure you use the preview post to check for errors in your post.
Hope my guide is clear as mud
let me know if your having problems.