For Black Ops 1, the trailer showed at the very END of the game, but the video was uploaded to youtube after the first few minutes of the game. So, the quickest presumable way to see the trailer would be to find it on youtube. Thankfully, the trailer is already uploaded onto youtube, only thing is, it's set to private. Here's the link: youtube.com/watch?feature=player_embedded&v=upCWKsa9Skw

I got this link from the black ops 2 website that was up and then taken down quickly this morning. If you keep refreshing that link, you'll definitely be one of the first people of the public to lay eyes on it when CALLOFDUTY's channel sets it to public.