As I see people add video to a blog post using embed code I can tell that they have not heard of oEmbed. If you want to quickly add a youtube video to your blog start by control clicking on the video. You can then copy the video URL. Go to your blog post and paste the video url into your blog post so that is on its own line.
You will have to scroll up or down if the images I have linked to above are hidden by the youtube video in my example.
For more on Embeds check out the codex.
Interesting, as I read through the codex I noticed that twitter was also supported. So if you add the link to a tweet on its own line then the tweet gets embedded into the blog post as shown below.
Watching Copyright Math http://t.co/DPwnL6Bi funny
— Gary Bertoia (@gbertoia) March 17, 2012