not all the people have the bandwidht to reproduce youtube HD

what are the other setPlaybackQuality('medium'); options?

i use 'low' but it dont work.

Can you help me please?

I tried getting the video to render in low, but it seems at large sizes -- like full background width in this case -- the player ignored what was specified in the JavaScript. I was disappointed I couldn't get it to cooperate b/c it would be nice for the video to load faster even on fast connections. In a case where you weren't concerned about quality -- such as an abstract or ambient background -- I really wanted to be able to set the quality to low and have the video load seamlessly. Thanks for your input.

YouTube's actionscript API reference lists the lowest quality setting as "small" rather than "low." It's working fine for me.

Instead of low, try "small."