When a video is uploaded to youtube, they compress the video and the audio. This results in a lesser quality and can not be avoided. This is why it is a must to get the highest quality to begin with before you upload.
When we process your videos for up load we make sure that the file as as large as allowed by youtube to insure the best quality. Videos uploaded from a camera program done by novice is usually highly compressed before it goes to youtube and then they compress it once again. This is why so many videos on you tube are of a low quality.