Download and install Audacity (it's free)
http://audacity.sourceforge.net/ - Open audacity and click the record button.
- Play your YouTube video and adjust the playback and record levels.
- Click the stop button and then "edit "undo" to get rid of the audio.
- Click the record button and play your Youtube video.
- Click the stop button in Audacity.
- Select: "File" "Export" and then select the folder you want to export the file to and "MP3 from the "save as type" drop-down menu.
Done!
It sounds a bit complicated but after you do it a couple times you'll find that it's simple and much faster than using the online converters. You don't have to download anything, and you don't risk infecting your computer.
Optional:
- Trim the beginning and end if necessary by highlighting the part you want to trim and selecting "edit" "cut" from the menu.
- Select "effect" "normalize" to normalize the audio level. (I usually normalize to -3 because I often import the audio into my DAW.)
*note: You may have to make sure that your computers sound card is set as the default input device.