You can upload your file using a link by clicking on 'Add file from Google Drive, Dropbox or Youtube' in the Media Library.
Make sure that your video on Youtube is Public or Unlisted. If the video is Private, we won't be able to retrive it.
Access Settings of your video and on the right side bar change its Privacy and click Save.
Copy a link to a video from the browser.
Google Drive Upload
1. If you see 'Only you have access' line under the file, you need to make it visible for us too, so we can retrive the file. First you need to click on Share button.
2. Click on Link for viewing > Create link > Save
3. Now anyone with this link can view the file. Copy the link, and paste it in our Media Library.