I download a lot of videos from many different sites, for this i use IDM in windows but in Ubuntu, i haven't found any down-loader which can deliver fast speed of downloading and is able to capture the videos from any video sites (not only youtube). Since the first day of switching to Ubuntu, i am trying to figure out what can be the best way to fulfill my wish??

"DownloadHelper" is one of the most useful mozilla browser's add-on for video download. I have use this to download videos from web. After download the add-on and install you should follow the steps to download video:

1. Video DownloadHelper icon in your toolbar like the image.

2. As soon as Video DownloadHelper detects a media you can download, the icon gets animated and colored, and a little arrow appears next to it, on the right.



3. Just start a video and click on the little arrow to choose the desired video.



 "DownloadThemAll" is another add-on like this and you can use this too.


Xtrem download manage is one of most popular download manager in Ubuntu. In bellow explain how to install xtrem in ubuntu.


wget -O xdman.zip http://sourceforge.net/projects/xdman/files/xdman.zip/download
Extract xdman.zip:

mkdir xdman
unzip xdman.zip -d xdman/
Enter to directory xdman/ and make exexutable file xdman.sh:

cd xdman/
chmod +x xdman.sh
To run:

./xdman.sh


Or you can install xtrem by this instructions:

sudo add-apt-repository ppa:noobslab/apps
sudo apt-get update
sudo apt-get install xdman

To run: 
sudo xdman