If you have an AdSense account, you can add Video Units to your site. Video Units are embedded, customizable video players featuring content from categories, individual content providers, or automatic keyword-based targeting. Here’s how to set up your player, assuming you’ve already signed up for AdSense and linked your accounts:

1. Go to New AdSense Player, fill out the information required, and choose the theme and layout.
2. Choose the content options. If you choose “Automated Content,” Google will fill the player with videos based on the content of your site. You can add keywords to target further.
3. Click the “Generate Code” button to get your HTML code and save the player.
4. Copy the code from the “Embed Code” section and paste it into your website or blog where you would like the player to appear.

source: http://youtube.com/youtubeonyoursite