Okey-dokey....This is how it is done:
Are you all sitting comfortably ? If you are, then I will begin !
Firstly you have to go to YouTube or any similar site and find a bit of music video that you might like to "embed" here.
Then you have to play that bit of video on that site using the local video-player.
Once it is playing you can then go to the address bar at the very top of your browser and highlight, copy and paste that address into the form, ( ignore the "share" button at the bottom of the form as sometimes the link that it provides might not work in the "embed" software here ), - BACK HERE - that that you will open when you click on the little "film" icon in the list of tags above the compose page. Once clicked on this form will accept that address, ( all of it ), and then you can click on the "OK" button attached to that form.
You will then find that the address URL is sitting in your compose page with the video-embed tags all around it.
Just add a bit of text to your post - to describe the video and why you are playing it - and then hit the "send" button at the bottom of the compose page.
"BINGO".... the video and it's embedded player will appear in your posting.
To play the video all you have to do is click on the arrow in the centre of the video-box and off it will go. ( You will then find that you have all of the normal controls of a video-player along the bottom of that box ).
( Also, of course, you will have to have sound capability in your computer ! ).
Have fun !
( Any questions about that, just send me an instant message ! ).