🚀 go-pugleaf

I'm attempting to download various videos from YouTube and other sites 
to a MacBook running Snow Leopard, using Safari and the current Real 
Player software.  I think I have the latest versions of the Real Player 
components; I've read their instructions and attempted to configure them 
properly; the Real Player apps open and seem to be alive -- but when I 
go to one of the video sites and attempt to capture what I'm viewing, 
nothing happens.  I can view the videos fine, but Real Player doesn't 
seem to recognize that anything is happening.

Any hints on what I may be doing wrong?  Or suggestions for alternative 
approaches to the basic objective?  Or are there some sites that are 
simply set up to frustrate downloading, including via the Real Player 
apps?  

[I appreciate this may be a question that gets re-posted all too often; 
but I have done some serious searching for ways to do this; and my 
impression is that the whole video streaming technology keeps evolving, 
and downloading methods that were once useful keep going obsolete.  
Also, for the record, I'm not attempting to pirate copyrighted or 
commercial entertainment videos; I just want to do some "fair use" of 
video information sources.]

(And as a sudden afterthought, will having Flash Blocker installed block 
video downloading, even if I can view Flash videos with no problems by 
clicking on them individually?)