If you insert a daily motion video and display it on a website which is https, the code inserted is http so the browser does not want to display it.
On daily motion they suggest to embed src without the protocol
Example:
<iframe frameborder="0" width="480" height="270" src="//www.dailymotion.com/embed/video/..." allowfullscreen></iframe><br /><a href="http://www.dailymotion.com/video/..." target="_blank">the title</a> <i>par <a href="http://www.dailymotion.com/..." target="_blank">Name</a></i>