Some web browsers have updated their security settings so that they won't display "mixed" content. Some links use the secure protocol, https, while the link to a video may use the standard http. The browser won't display potentially "unsafe" content in a "secure" page.
There is a little shield or similar symbol in or near the URL bar - click it and select the option that allows the display of the video.
Note that this is a browser setting - we do not have any control over it.