Playing movie problem in widet blurprint

I used media player and related assets to play video in Widget blueprint. But it didn’t work.

I could confirm that the movie played correctly in the design screen of Widget BP. However
I play the game, The movie won’t starts and stay black.

Now, I found the Media player asset mybe wrong. When I reopen the asset after playing, It doesn’t hold movie asset.

If you know why and how to fix, please let me know.

Thank you!