YouTube Videos
Youtube
http://www.youtube.com/t/terms
Content is provided to you AS IS. You may access Content for your information and personal use solely as intended through the provided functionality of the Service and as permitted under these Terms of Service. You shall not download any Content unless you see a “download” or similar link displayed by YouTube on the Service for that Content. You shall not copy, reproduce, distribute, transmit, broadcast, display, sell, license, or otherwise exploit any Content for any other purposes without the prior written consent of YouTube or the respective licensors of the Content. YouTube and its licensors reserve all rights not expressly granted in and to the Service and the Content.
Youtube standard License
By default all videos are subject to the YouTube Standard License. As you can see on the About tab of a video, the License details are displayed. You may have to click on the "Show more" button to expand that section.
Downloading from Youtube
If a download is available, then a download link will appear in the License section. Downloads are only available from very specific channels that have special partner agreements with Youtube.