Go >HERE and you will find the information you are looking for.
Click the link below. Everything else should be self-explanatory:
You can download the YouTube vid through torch.
I personally use these websites to download and convert youtube videos :https://9converter.com/
I'm sure that you could find millions solutions with the help of Google, but guess, you want to get proven methods. So, i will try to help,
First, read Comparison of YouTube downloading apps from Wiki - check their features and decide what features you need mostly.
If you don't need any Pro features and maybe not ready to pay for app, your best solutions - web services. There are so many offers. I had been using keepvid for long time, but thy closed service, so i found some alternative of also dead YouTube-mp3.org - www.youtubemp3org.online/ Works good, l'm satisfied
Click the link below using this free and fast youtube downloader.
You can use mp3musics