To embed high quality YouTube video you need to append &ap=%2526fmt%3D18 to your embed string. Of course if you use WordPress, you can use Smart YouTube plugin which will do this automatically for you, among other cool things. Watch the difference in example below. First is the low quality version, standard size 425x344.Now this is a high quality version in 480x360. Not only the resolution is better but quality too. Smart YouTube supports different sizes for normal an HQ videos.