Downloading a video you don’t intend to distribute further is legal. “Fair Use” also makes downloading some videos legal for commercial means, as long as you comply with its guidelines. Using something other than the download button YouTube provides can be seen as a breach of its ToS. However, we’ve yet to hear of someone actually getting into trouble because of this. We strongly believe that downloading a video from a site that shares them to be consumed at a later time or in offline mode serves the same purpose as timeshifting, so it should fall under fair use. The case of Betamax already sets a precedent. Downloading videos that claim no copyright is therefore legal. If a video doesn’t hold the Creative Commons license, we advise that you ask its creator for permission first before downloading.