Download YouTube and other videos using youtube-dl

You don't need a browser extension to download videos from popular sharing sites like YouTube or SoundCloud. youtube-dl gets the job done with minimal effort on the command line and is available for all platforms while supporting 1000+(!) sites.
To get youtube-dl you can either go to https://github.com/rg3/youtube-dl and download the appropriate version for you or if you have PIP installed simply by calling: pip install youtube-dl.

Note: youtube-dl is a tool based on Python. If you're on Windows you don't need Python installed already as the download ships with the required Python libraries for windows.

Optional: If you want to extract audio from for example music videos you will need to download ffmpeg and place its binary and libraries in the same folder as youtube-dl. You can get the latest version of ffmpeg here: http://ffmpeg.zeranoe.com/builds/.

To start using youtube-dl here are some examples:

List all supported sites:
youtube-dl --list-extractors

Simple download of a video:
youtube-dl "<URL>"
Note: The same works for playlists!

Extract mp3 audio from a video:
youtube-dl "<URL>" -x --audio-format mp3
Note: For this to work you need the optional ffmpeg part above!

List available formats for a video:
youtube-dl "<URL>" -F

Then use a lower-case 'F' and the 'format code' to retrieve a specific format:
youtube-dl "<URL>" -f 123