When are they offering draws and when are they resigning?

Ok, I have this really weird problem. I was going through some videos of chess games. At the end of the game, the players always shook hands, but I couldn't figure out if one of them was resigning or offering a draw. I mean, is there a way of telling from the videos, (if the position on the board is unclear of course) if the game is drawn or someone is resigning?

not really, I've seen two players smile and shake hands over a drawn game...

To put it in perspective, when Anand and Topalov shook hands at the end of their 8th game in the just concluded World Championship match, several people (myself included) thought that they had agreed on a draw. When I saw the score of 1-0, I was shocked...clearly not everything is obvious unless it is put in writing. I guess shaking hands is just a polite and gentlemanly conduct and as such doesn't necessarily indicate the result of the game.

Not always. Topalov resigned in a drawn position against Carlsen a couple years ago.

When someone smiles and shakes hands it doesn't necesarily mean a draw. I shake hands with my opponent after an OTB game no matter the results.

Generally, they do announce the results

it is not really nessesary to guess with Magnus Carlsen.

Kosteniuk beats Magnus Carlsen http://www.youtube.com/watch?v=WeyXKTVYenA

watch his reaction as he loses priceless. 6:33

So unfortunately doesn't exist more players, who jump and shout "Gegen diesen Idioten muss ich verlieren!".

Yeah, sometimes even Grandmasters misjudge the position. And let's not forget Grandmasters that are known for early resigns, such as Ivanchuk.