You can’t just using Axel to download Tube8 videos. First, you must get the cached video link on the server, in this case Tube8’s CDN Server. How to obtain that?
You can use Google Chrome Download Video Web extension or Quick Play extention to obtain the cached video link. Unfortunately, since I checked it on 19th of December the Download Video Web is unavailable. So, you can install Quick Play extension instead.
The lack of this Quick Play extension is sometimes it gets the right cached video link and sometimes not. This kinda frustrating. As an alternative you can use get-flash-videos program.
How to Install get-flash-videos
sudo apt-get install libwww-mechanize-perl libxml-simple-perl
sudo dpkg -i get-flash-videos_1.21-1_all.deb
You can also follow another instruction about how to use get-flash-videos here.
How to Obtain Cached Video Link on Tube8 CDN Server
Open the Terminal and, for example, type:
Wait until the “Which filename would you like to use?” appears and type 1 or 2 is up to you, then Enter.
Boom! You get the direct download link of Tube8 flv format video. Copy that http://cdn1.public.bla bla.. and download it with Axel for quick and simultaneous connection download.
You can read how to install and use Axel if you have no idea what Axel is.