When you post a video from YouTube or Vimeo to the feed, use just the ID and not the full URL.
We add the proper embed scripts behind the scenes for you. When you want to post a video the feed, copy/paste only the ID. So for example, to embed the following YouTube video, use only the bolded ID as shown below:
www.youtube.com/watch?v=UCFg9bcW7Bk
For a Vimeo video, use only the bolded ID as shown below:
vimeo.com/83651159