In section 5B of YouTube's terms of service, it says: "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." According to the above section of YouTube's T.O.S., videos on their site shouldn't be downloaded unless a download link of the video is provided. I use TubeMate, a third party android software to download videos from YouTube. Is this a sin?