How to convert HD video to MP4/YouTube/MPEG video

Maybe some people will ask: what is HD video and why it can be widely used?
Answer:
High-definition video or HD video refers to any video system of higher resolution than standard-definition (SD) video, and most commonly involves display resolutions of 1280×720 pixels (720p) or 1920×1080 pixels (1080i/1080p).
Nowdays, HD is becoming more and more popular as the following reasons:
1.HD DVDS, together with equipment to play and record them, are available now, stimulating the public appetite for HD.
2.PC displays with HD quality potential are becoming widely used, which will acclimatise the public to HD.
3.Large flat LCD screen with HD resolution are becoming readily available at prices which the public seems prepares to pay, providing the means to view HD.

While, HD video also has some inconvenience to use, such as, we can’t edit them
in Windows Movie Maker or some other edit software; can’t put them into portable devices directly , like iPod, iPhone, Zune, Creative Zen and so on; can’t share videos with friends on youtube, myspace and other online video website. etc.