1. Go to your selected video-sharing/video-hosting site and copy the video URL.
2. Click the YouTube icon from formatting toolbar (see image below):
3. Paste the copied link on the text box that will appear after clicking the icon.
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Bear in mind that the supported video-sharing platforms are exclusive to YouTube, DailyMotion, Metacafe, MySpace Video, Veoh, Revver, and Vimeo.