Help.? Enabling Youtube HD on?

Ok, so I use Im too HD video converter since I bought it. I currently post NBA videos and other videos on youtube. What I'm asking is how do I enable the videos to play in HD? Ive tried everything. Ive even put &fmt=18 at the end of the URL. It plays in HD, but it wont save so it can keep playing whenever somebody clicks it. Points for best answer?