Converting the audio from a YouTube video is easier than you think. Follow these instructions to copy the music you found on YouTube to your iPod.
Steps

Step 1. Find a high-quality YouTube video
Although many videos may have the song you want, there are some that have a better quality than others.

Step 2. Copy the link of this video
Just select the link and press CTRL + C to copy.

Step 3. Convert the file using free file converting sites
Sites like zamzar.com, freefileconvert.com, or mediaconverter.org will allow you to put the link and select what type of format you want to convert it to (mp3 or mp4 works in iTunes), and they will send it to your email.
Do not pay for this service

Step 4. Wait for the mail
This may take an hour or more depending on the size of the file and the amount of work on the server.

Step 5. Download your email file
Just right-click on the file and select "Save" or "Save As."

Step 6. Click on the file you just downloaded to change the song information
For Windows, go to Properties> Details; On a Mac, go to "Get Info." Put the correct data of the song.

Step 7. Move the file to the appropriate folder in iTunes
If you have iTunes automatically organize your music folder, you could open iTunes and just drag the file into the library.

Step 8. Hear the song
Make sure it can be heard well. While you're at it, you can modify the information, such as title, artist, album, genre, etc.; You could also look for the cover of the cd and put it to the song.

Step 9. Synchronize your iPod
You already have a new song on your iPod!
Advice
- Don't download more than 5 songs at the same time; you will only encourage your system.
- You don't need to keep your songs on your computer after transferring them to your iPod, unless you want to.
- Most sites have a download limit of 10 songs.