Download videos from online resources, such as YouTube, Dailymotion, etc..

Among the most popular video hosting resource on the web is YouTube, being the third most popular website in the world. Sometimes we find ourselves in need to download a video in order to be able to watch it offline. 

There are several online services which allow us to save a copy of our favourite videos but not all of them allows you the option of downloading in different qualities and formats.

Quick Links for downloading YouTube..
VIDEO: One of the easiest ways to download a video from YouTube is by visiting the following URL:

http://en.savefrom.net/1-how-to-download-youtube-video/

or 

http://vidconv.net

MP3: Downloading an MP3 version of a video can be done by visiting the following URL: 
http://www.youtube-mp3.org

Other Downloading resources and methods..
By visiting the website at http://en.savefrom.net you will find a number of media hosting resources being supported. Most popular among them, besides YouTube, is Dailymotion, Vimeo, Facebook, soundcloud and many others. 

On the other hand you might want an approach which involves scripting and/or programming. In that case I advice you to take a look at the following resources:
http://rg3.github.io/youtube-dl/download.html
https://calomel.org/youtube_wget.html

Also, the following perl script will do the job for you in a fast and convenient way. 

#!/usr/bin/perl

use strict;
use warnings;

#### Two arguments ############################
##     $1 YouTube URL from the browser
##     $2 Prefix to the file name of the video (optional)
##

## Collect the URL from the command line argument
my $url = $ARGV[0] or die "\nError: You need to specify a YouTube URL\n\n";

## Declare the user defined file name prefix
my $prefix = defined($ARGV[1]) ? $ARGV[1] : "";

## Download the HTML code from the YouTube page
my $html = `wget -Ncq -e "convert-links=off" --keep-session-cookies --save-cookies /dev/null --no-check-certificate "$url" -O-`  or die  "\nThere was a problem downloading the HTML file.\n\n";

## Collect the title of the page to use as the file name
my ($title) = $html =~ m/<title>(.+)<\/title>/si;
$title =~ s/[^\w\d]+/_/g;
$title =~ s/_youtube//ig;
$title =~ s/^_//ig;
$title = lc ($title);

## Collect the URL of the video
my ($download) = $html =~ /"url_encoded_fmt_stream_map"([\s\S]+?)\,/ig;

## Clean up the URL by translating Unicode and removing unwanted strings
$download =~ s/\:\ \"//;
$download =~ s/%3A/:/g;
$download =~ s/%2F/\//g;
$download =~ s/%3F/\?/g;
$download =~ s/%3D/\=/g;
$download =~ s/%252C/%2C/g;
$download =~ s/%26/\&/g;
$download =~ s/sig=/signature=/g;
$download =~ s/\\u0026/\&/g;
$download =~ s/(type=[^&]+)//g;
$download =~ s/(fallback_host=[^&]+)//g;
$download =~ s/(quality=[^&]+)//g;

## Collect the URL and signature since the HTML page randomizes the order
my ($signature) = $download =~ /(signature=[^&]+)/;
my ($youtubeurl) = $download =~ /(http.+)/;
$youtubeurl =~ s/&signature.+$//;

## Combine the URL and signature in order to use in Wget
$download = "$youtubeurl\&$signature";

## A bit more cleanup
$download =~ s/&+/&/g;
$download =~ s/&itag=\d+&signature=/&signature=/g;

## Print the file name of the video collected from the web page title for us to see on the CLI
print "\n Download: $prefix$title.webm\n\n";

## Download the file using Wget and background the Wget process
system("wget -Ncq -e \"convert-links=off\" --load-cookies /dev/null --tries=50 --timeout=45 --no-check-certificate \"$download\" -O $prefix$title.webm &");


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