More and more sites have started automatically using secure connections since the Edward Snowden revelations. It's a good thing because it helps safeguard our privacy. I'm not an expert or anything, but I assume both addresses land on the same web page but https uses an encrypted connection whereas http is open for anyone to snoop on.
As for other videos, the forum software doesn't recognise them all unfortunately. I believe every different player requires a specific plugin enabled on this site. ITV changed their videos (from youtube to something new) a while back so we were no longer able to embed their videos. I don't know if that's still the case or if they went back to using youtube.