To create custom feeds, specify the tag or username you wish to subscribe in the URL as described below.
RSS Feeds for Tags and Users
To create an RSS feed for your favorite tags or users, simply enter the tag or username as specified in the below URLs. You can then add this URL to your newsreader. Please note, you will need to create a feed for each individual tag or user you wish to subscribe to.
For example, if you wanted to create an RSS feed for the tag "monkey," you would enter: feed://www.youtube.com/rss/tag/monkey.rss
feed://www.youtube.com/rss/user/[insert username here]/videos.rss
For example, if you wanted to create an RSS feed for the user "YouTube," you would enter: feed://www.youtube.com/rss/user/youtube/videos.rss
タグやuser id によってカスタマイズできると。