I've had it with people using the "embed youtube video into post" function the wrong way. Everywhere I look: videos that won't play and quite frankly, I can't blame you. It isn't self-explanatory. However I can't fix this in each post and I won't explain it to each new user, so I will explain it here once and for all. 
Imagine you want to post a video of a kitten riding a turtle. The URL is this:
External Content
www.youtube.com
Content embedded from external sources will not be displayed without your consent.
Through the activation of external content, you agree that personal data may be transferred to third party platforms. We have provided more information on this in our privacy policy.
[*youtube]
External Content
www.youtube.com
Content embedded from external sources will not be displayed without your consent.
Through the activation of external content, you agree that personal data may be transferred to third party platforms. We have provided more information on this in our privacy policy.
http://www.youtube.com/watch?v=
External Content
www.youtube.com
Content embedded from external sources will not be displayed without your consent.
Through the activation of external content, you agree that personal data may be transferred to third party platforms. We have provided more information on this in our privacy policy.
The problem: you put the entire URL between the brackets you silly bear! Try to only put the Video ID between the brackets, it's the code after the "?=" in the URL and in this example:
[*youtube]JS-QX061KHU[*/youtube]
Without the * that I used for demonstration purposes the video will display correctly:
External Content
www.youtube.com
Content embedded from external sources will not be displayed without your consent.
Through the activation of external content, you agree that personal data may be transferred to third party platforms. We have provided more information on this in our privacy policy.
Happy posting!