I think you can guess where this is going...
1) Open a file-explorer (e.g. Konqueror, Nautilus) and open /tmp
2) Open youtube in a browser. e.g. FireFox
3) Watch /tmp in the file explorer and you should find a file called something like "FlashITXfHE". This is your .swf file containing the youtube video.
4) Make sure that the video is completely loaded (that's when progress bar is completely red)
5) Copy/Paste the "FlashITX..." file and rename it to something like "video_backup_youtube.swf"
That's it.
