Please kindly do not hijack the thread even if the problem you are facing is similar to the original poster. For more information kindly read this article:
Kindly, open up a new thread with the detailed information and we will be more than happy to do our best to help you around regarding the issue.
Regarding the question, unfortunately, you cannot add directly to the object as the code is auto-generated in the lightbox and the video shows with the usage of MEjs library embedded in the WordPress itself.
I think you will be better off to use a lightbox plugin that you can add custom code inside. That way you can add the Embed object for the lightbox either. Unfortunately, our lightbox does not support that.
I did a Google Search regarding this and you may consider checking those plugins. Needless to say that those are not our official recommendation and just a helper to get you started.
For additional help kindly open up a separate thread.