In order to embed videos in a Blog/CMS post, please carry out the following steps:
1) On the video sharing platform of your choice (such as Youtube / Vimeo) click on share/embed and get the embedding code (not the URL!). Please copy this embedding code.
2) In the Blog/CMS post editor please click on the <> icon on the top left of the text editor to enter the HTML mode of the editor
3) Paste the embedding code from before and save the post.
4) Responsive Size: In the widget menu of the Muse Blog/CMS (as well as the Recent Posts and Post Field Loader widgets) there is an option for responsive videos. If this option is checked, your embedded YouTube or Vimeo videos will automatically resize responsively, according to the width of their container (column / post / field).