Recently I have tried to get high quality RTSP Streamng using gData API
I have got only one clue from google, http://code.google.com/intl/ko/apis/youtube/2.0/reference.html#formatsp
Here it says I can get the video url only for low resolution (176x144), Is there any way of archiving the url for high quality video?
See this: http://code.google.com/p/android-youtube-player/
This can easily be ported over to another platform, although currently is in Java / Android.
You get high quality video from this, have been looking for this for a really long time. The trick is to make a web request to YouTube requesting the different available streams, you actually get very personalized URL's, often directly from your ISP, very cool.