Videos issue / black side bar

Hello everyone, 

I’m having a problem with a client project.

We have produced several modules presenting slides including videos (.mp4).

When we export these modules and view them (regardless of browser), a black bar appears on the video side when we change the size of the page where the module is opened. For each test on different computers or browser, the black bar are not present all the time or at the same location.

I can observe that bars appear when I resize my browser window.

We used the client’s player, the modern player, and we don’t have the ability to block the opening of the module to the optimal size.

How to avoid these black bars?

I thank you in advance for your help,