YouTube-dl is an open source command line application designed to download audio and video content from YouTube and other video streaming websites. It supports downloading videos in various formats and resolutions, as well as extracting audio from videos. Additionally, it can also be used to download full playlists and subscribe to channels. YouTube-dl is a versatile and powerful tool that can be used to download music, video lectures, podcasts, audio books, and much more. It is extremely easy to use and is available for free for Windows, macOS, and Linux.
Youtube-DLG is an interface to youtube-dl. It still requires youtube-dl to work.
Bundleware The default Windows installer contains Opencandy. A version without third-party offerings is available in the download options.
Discontinued The extension currently does not work in Firefox 57, it still works in lower versions: https://forums.informaction.com/viewtopic.php?f=6&t=23325&sid=00474d828d2582731536b4ea5146d5af
Bundleware El instalador contiene OpenCandy. Tenga cuidado durante la instalación: https://alternativeapp.info/discussions/applications/11718/be-careful-in-the-installation/
Bundleware The desktop software contains adware.
Discontinued It seems that the project is no longer maintained and the official website is no longer available. The latest version, v2.7, can still be downloaded from Softpedia and the source code is available on SourceForge (v2.5).
By RemovedUser · Sep 2017
Buena herramienta de línea de comandos que hace lo que dice: descargue videos (y, opcionalmente, conviértalos a otros formatos, incluida la captura de la parte de audio) de YouTube y muchos otros sitios web. Un inconveniente: no puede descargar clips de música de YouTube; muestra un mensaje de error. Extraño, ya que PUEDE capturar la parte de audio solo de un video en YouTube; pero aparentemente no puede manejar un archivo de solo audio en YouTube. Aparte de eso, funciona bien. [Editado por LB7979, 2 de septiembre]
This is the best program I could find.