Here the similar steps to save YouTube videos on your computer from Opera cache, try the following steps:
1. Watch full Youtube video in IEbrowser.
2. Don’t close the IE browser, watch till the end of video.
3. In the Internet Explorer click [Tools] – [Internet Options…] – [Temporary Internet files] – [Settings…] – [View Files…].
4. Sort the files based on Size, find the file that probably that you watch.
5. Choose the proper file
6. Copy and paste it to your desktop
7. Rename the extension to .flv
8. You can download the free FLV Player from brothersoft.com
9. Now play that flv file with the FLV Player