Make sure you embed the HTTPS version of the URL and in case you use custom BBCode, it should embed as HTTPS and not HTTP.
You can also try adding <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests"> to the headinclude template.
Thanks Dave
These are the two codes i have in my template bbcode.Do any of these need an update .
<vb:elseif condition="$provider == 'vimeo'" />
<object class="restrain" type="application/x-shockwave-flash" width="640" height="360" data="//vimeo.com/moogaloop.swf?clip_id={vb:raw code}">
<param name="movie" value="//vimeo.com/moogaloop.swf?clip_id={vb:raw code}" />
<param name="wmode" value="{vb:raw wmode}" />
<!--[if IE 6]>
<embed width="640" height="360" type="application/x-shockwave-flash" src="//vimeo.com/moogaloop.swf?clip_id={vb:raw code}" />
<![endif]--></object>
<vb:elseif condition="$provider == 'dailymotion'" />
<object class="restrain" type="application/x-shockwave-flash" width="560" height="349" data="https://www.dailymotion.com/swf/{vb:raw code}">
<param name="movie" value="https://www.dailymotion.com/swf/{vb:raw code}" />
<param name="wmode" value="{vb:raw wmode}" />
<!--[if IE 6]>
<embed width="560" height="349" type="application/x-shockwave-flash" src="https://www.dailymotion.com/swf/{vb:raw code}" />
<![endif]--></object>
We are using 4.2.1
I am also thinking it may be a flash issue
--------------- Added 1519551600 at 1519551600 ---------------
Update
Ok i have fixed this and its just a flash issue.
In google chrome I had to go to settings and then content settings.I then clicked on the flash icon and it gives you an option to add a website.As soon as i added my website it all worked.
I am not sure why you have to do that but there must be something in the firefox browsers also where you have this option.