Keepvid also let you download only sound as mp4 or convert the sound to mp3.
For facebook there is no need of a downloader, just change "www" by "m" on url so you watch the video as if it was on your smartphone, and right lick on video,you will the option to download it. That's all for facebook videos.
You need to install JAVA and allow it to be executed when you try to download a video using keepvid site.
Probably your browser is 32 bits so you just need to download and install 32 bits version of JAVA:
If you search for java on this blog, on right side you have a search box, i think i made another post about java download and install. Right now i'm not sure of the correct url to download full java software needed since it is givng me an sql error...
"An error occurred reading the asset. [com.openmarket.basic.interfaces.AssetException: SQL statement failed -105:] .
An error occurred reading the asset. [com.openmarket.basic.interfaces.AssetException: SQL statement failed -105:] .
An error occurred reading the asset. [Asset jDownload_P:0 does not exist in Content Server.] ."
From there if it is the right url, you can choose language and version of java needed.
Best thing to do, is uninstall all versions of java you have and make a fresh install just of 32 bits version, for most of us we do not need java 64 bits, unless you use internet explorer 64 bits or another 64 bits application (having windows 64 bits won't use java 64 bits, is the 64 bits application that will need the 64 bits java)
bla bla bla
By the way, lot of people use plugins for firefox to download videos, on smartphones you also have TubeMate from http://tubemate.net, and there are some other online sites abble to download videos that keepvid can't but you will have to look for them on google and try them (some are really useless...)