очень просто. Есть хороший сервис youtubex.com
На странице есть поле, куда вставляешь ссылку на youtube-видео, например _http://youtube.com/watch?v=Q275Qh4ESao, затем нажимаешь кнопку Get Video. Через некоторое время появляется прямая ссылка на флэш-ролик, который можно скачать как обычный файл.
Вообщето, keepvid.com тащит не только с youtube, но и с десятка других сервисов онлайн видео.
Посмотрел на самом сервисе(онлайн) видео полностью(чтобы закачалось), залез в кэш броузера(IE там или Firefox, или еще чего), нашел большой файл, скопировал куда-нить, добавил расширение .FLV если небыло у временного файла, и смотрю его локально.
И ничего никуда не надо лезть и повторно качать видео, но уже качалкой.
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