You might try to download videos on videolecture but it didn't let you, didn't you?
I want to explain a method for downloading such non-easy downloadable videos.

Download and install HiDownload (video stream downloader) , there are some download links in this page.

Go to the video page, for example please see this page.
Find this link : Launch in a standalone WM Player, and copy its URL, for example for this video , this is the video link.

Give that URL you found in the previous step to your HiDownload and forget about it, sometimes it takes time to start download, but be patient. I've downloaded some videos before, and it worked for me. If it doesn't start, search in Google for an alternative video STREAM
downloader, one of them should work.