The preview or build mode does not support playing of video, which is why we show a preview image.
Sometimes, even when the format is supported, the video host does not provide a preview image we can display.
When that happens you will see a grey box with a play button. This is only displayed when building.
This is how video shows when there is not a preview image supplied.
If you would like to see the video, within your StickyAlbum or StickyFolios publish your Folio then open the link to in a new browser window.