Retention Time and Specific Videos Caching

I have specific videos from my channel on youtube that I would like to cache forever. Can I set that somewhere. Maybe a specific line for each video or something.

Also how long does videocache hold videos and why does it seem to load only a quarter of the video when you click on one then slowly load the rest?

Also, is there a script that anyone knows of or some other way to crawl certain websites over night so they are cached. Like go and load the top 100 videos on youtube or something like that.

thanks