One other thing to try because YouTube changed their security method some time ago is to remove the "s" in the url. For example, if you have a YouTube loaded, you can capture the url in the browser address bar. It will look something like this
https://www.youtube...
Remove the "s" from the https so it looks like this:
http://www.youtube...
...and just paste the entire url into your forum post. Your video should show in most web applications that support web videos.
For example, if I just paste muebe's browser url into this post, it looks like this:
However, if I remove the "s" in the same url, it displays properly, like this: