Forget re-uploading what you’ve already backed up. That’s a sucker’s bet. 🙂
Instead visit youtube.com/upload, then click “Import your videos from Google Photos.” You’ll see a browser like this that lets you pick one or more videos, then click “Select” to add titles, etc. & publish them.
Bonus tip: To see all the videos in your Photos account, click the search field, then click the “Video” tile (or just bookmark photos.google.com/search/_tv_).