Non-functioning embed code is often due to a CMS not allowing <script> tags, or a WYSIWYG visual editor breaking the embed code.
Wordpress.com doesn't allow <script> tags (but self-hosted wordpress sites do). Many self-hosted wordpress sites have a WYSIWYG visual editor enabled for posts, but you'll need to make sure that the plain html editor is enabled, and that someone doesn't come in and accidentally open the post w/ the visual editor, which will break the embed code.
Alternatively, you could try using the Universal Subtitles auto-embed script (link needed), which will add the video-widget to every video on a page.
More information on embedding and widget script: https://github.com/pculture/unisubs/wiki