Hi there I have a question:

I created a custom movie and converted this movie to a .bik file. To be able to see that custom movie, it's locally in the "Portal 2\portal2\media" folder. I also created the entity "vgui_movie_display" and linked with the custom movie. When I run this test map I can watch that movie.

I also would like to realize that steam user also can see the custom movie. But there is a problem: If steam users want to play this test map they are looking to a blank area. I think when I uploaded the map to the steam workshop the custom movie was not uploaded.

Is there a way to avoid this issue?

Custom .bik video won't work when packed into .bsp. So there's no way for workshop players to see it this way.

But there's a workaround. You can convert your video to images and then create an animated texture which can be packed into your map file and so works in workshop.

OR you can put a "custom assets" download on the workshop description (in which 100% of the people reads it).

But yeah I recommend the other guys solution (more casual)