I can not preview video

Hello, I’m trying to preview video when I add it to the design you do not see anything.

I am doing something wrong??

Thank you

Video previews only work with formats your browser can play directly - specifically for Chrome/Firefox H264 MP4, and WebM.

Other formats will show a black screen. You can click on the black space to skip the video.

Gracias, fue muy util tu respuesta.