How to download videos from youtube and other sites

There are many tools available for downloading video from sites like youtube and metacafe etc. but small command line downloading tool youtube-dl
fulfil most of the requirements . It requires Python interpreter, version 2.6, 2.7, or 3.3+ , and it’s not platform specific you can use that tool anywhere its just require that python interpreter .
best thing about youtube-dl is you can perform many post download task just by passing arguments before stating download
-x, --extract-audio convert video files to audio-only files (requires
ffmpeg or avconv and ffprobe or avprobe)
--audio-format FORMAT "best", "aac", "vorbis", "mp3", "m4a", "opus", or
"wav"; best by default
--audio-quality QUALITY ffmpeg/avconv audio quality specification, insert
a value between 0 (better) and 9 (worse) for VBR
or a specific bitrate like 128K (default 5)
--recode-video FORMAT Encode the video to another format if necessary
(currently supported: mp4|flv|ogg|webm)
-k, --keep-video keeps the video file on disk after the post-
processing; the video is erased by default
--no-post-overwrites do not overwrite post-processed files; the post-
processed files are overwritten by default
It’s support almost 65+ sites
Supported Websites ..
youtube , metacafe , dailymotion , video.google:search , photobucket , Yahoo , screen.yahoo:search , DepositFiles , facebook , blip.tv , blip.tv:user , vimeo , myvideo , ComedyCentral , Escapist , CollegeHumor (CURRENTLY BROKEN) , XVideos , soundcloud:set , soundcloud , InfoQ , mixcloud (CURRENTLY BROKEN) , stanfordoc , MTV (CURRENTLY BROKEN) , Youku , XNXX , YouJizz , Pornotube , YouPorn , plus.google , arte.tv , NBA , WorldStarHipHop , justin.tv , FunnyOrDie , Steam , ustream , RBMARadio , 8tracks , keek , TED , MySpass , Spiegel , liveleak , ARD , ZDF , Tumblr , Bandcamp , RedTube , Ina , Howcast , Vine , Flickr , Teamcoco , XHamster , Hypem , Vbox7 , Gametrailers , Statigram , Break , Vevo , Jukebox , Tudou , CSpan , Wimp
Installation
Linux , Ubuntu , Mint , Debian
$ sudo apt-get install youtube-dl
MacOSX
$ brew install youtube-dl
OtherOS , user manual installation
$ sudo curl -o /usr/local/bin/youtube-dl http://youtube-dl.org/downloads/2013.07.08.1/youtube-dl
$ sudo chmod a+x /usr/local/bin/youtube-dl
For windows
http://youtube-dl.org/downloads/2013.07.08.1/youtube-dl.exe
Download : http://rg3.github.io/youtube-dl/download.html