The owner (uploader) can download the video again. Depending on the server settings you are allowed to download the original and or the transcoded version.

Click download

If there is an original, you will get the following choice

Make a selection an continue with OK. In the background the server prepares a zip file for you.

Don't navigate away, wait until you see

When you click on download a zip file with video and metadata will be downloaded.

The name of the zip file is the same as the title.