This article describes how to upload a video package to a File Activity. This is only possible when importing activities, since you must upload a video file to an activity created through the user interface.
Go to the Activity's Properties page
Click on the title of the activity
Click on the Properties tab
Upload Video File
Click on the "Upload a new file" link. In the pop-up window, click on the Choose File button and select the file from your computer. Click the Save button.