TEN - Video Catcher allow to embed Youtube and Dailymotion videos easily. That's the lightest plugin you can find for WordPress.
If you play a YouTube video, look at the URL - it will probably looks something like this...
The video ID is the list of letters and numbers after
v=, in this case
If it's a dailymotion video, the URL looks like to...
You have two way to define de ID of the video.
First, the easier is to copy all characters after the last /, the result is :
Second, you can clear the video's title to get the ID, like that :