have more tools to use in this case and I can suggest you use add ons in Firefox to download videos from youtube.com. it's very efficient and you can try to search "youtube video download" in firefox addons box search.
FOr me, I am comfortable using IDM ( Internet Download Manager). I used to use YTD (youtube downloader), but lately, I am having trouble downloading videos for some reason. Since then, I am now using IDM it is easy and very convenient to use. SO far I don't have any issues using the tool. But I am still open to try other video downloader tools. So anyone, who know other tools, feel free to share it here. I will be more than glad to try it. Thank you!
I use Free Download Manager. Basically, you can use it to download almost anything from the internet. Manage your downloads, queue, schedule, set a bandwidth, etc. It has pretty good looking interface. It's the best downloader I've used after giving up on YTD and other shitty software for downloading stuff. If you want a quick and dirty way, there are a lots of add-on for every browser.
I had the same problem of trying to find a video downloader for youtube. I had been using YTD (Youtube Video Downloader) but somehow it stopped after updating it. I came across another one SavefromNet, it is working good but the problem it cannot download all the videos. So far so good, it's working for me.
Try using Tubemate, if you are using an android smartphone I think this one is pretty good to use. This app is not available at the google play store, but you can still download this .apk file. You'll just need to modify your settings restriction allowing it to be uploaded on your mobile device.
While viewing the video, in your address bar, add the word "magic" on the link of the video then press enter. You'll be redirected to a site wherein you can choose option what type of download you want.
How about the youtubedownloadapp? All you need to do is install the app first and copy paste the link of the video. Downloading usually varies on how long is the video. Also if you don't ask if you want to convert a video into an mp3 file try going to youtube2mp3.com it is a great with a very simple user interface, I'm pretty sure you'll have no problem downloading those mp3files. The steps are just the same, copy the link and convert. This usually takes a shorter time than downloading a video ofcourse hahaha. I hope I did help you with your problem.
If you're using an android phone, OGYoutube is my top choice followed by Tubemate. If you're using your browser then there are several Firefox add-ons who will allow you to do this. If you use another browser, saveform will do everything online for you and you won't have this problem.