Oh well, you live and learn.
I have to point out, however, that the Terms of Use of YouTube prohibit downloading of material:
The content on the YouTube Website, except all User Submissions (as defined below), including without limitation, the text, software, scripts, graphics, photos, sounds, music, videos, interactive features and the like ("Content") and the trademarks, service marks and logos contained therein ("Marks"), are owned by or licensed to YouTube, subject to copyright and other intellectual property rights under the law. Content on the Website is provided to you AS IS for your information and personal use only and may not be downloaded, copied, reproduced, distributed, transmitted, broadcast, displayed, sold, licensed, or otherwise exploited for any other purposes whatsoever without the prior written consent of the respective owners. YouTube reserves all rights not expressly granted in and to the Website and the Content.