How to have video thumbnails in Alfresco 4.1.x?

For a project, I had to find how to generate thumbnails in Alfresco. My constraint was that it had to be implemented in 4.1.x and I remembered that there was something provided in Alfresco 4.2.x. I checked the ZIP of the installation file of Alfresco 4.2.x and I discovered 2 interesting files in the folderĀ /web-server/shared/classes/alfresco/extension: