ClipConverter is a free resource that enables you to convert media files. It is one of the best and most reliable free converter and is quite fast.
The website provides simple conversion instructions as seen below.
How to convert and download a YouTube video:
1. Paste your YouTube URL at ‘Media URL’ and press Continue.
2. Select the format and the options for the conversion. The default options are for most videos a good setting.
3. Press the ‘Start’ button at the bottom to start the conversion.
4. This may take several minutes. After the conversion is finished you can download the converted file.