Hi Grzegorz,
Might be easier if we can see the issue on this one, could you zip up your project files and share them so that I might take a look.
The forum will support a file size of up to 10mb, if your project is larger than this you could use a service such as Google Drive or Dropbox and share the URL in your post.
See also;
- YouTube Support : Upload Video
- Forum User Guides : How to embed a YouTube video within your post