Here the similar steps to save YouTube videos on your computer from Opera cache, try the following steps:
1. Watch full Youtube video in Opera browser.
2. Don’t close the Opera browser, watch till the end of video.
3. Locate the cache file at following folder C:\Program Files\Opera\profile\cache4
4. Sort the files based on Size, find the file that probably that you watch.
5. After the streaming has completed, go back to the Opera cache folder at C:\Program Files\Opera\profile\cache4. Note: Do not close the tab in which you viewed the YouTube video. There should be a large tmp file in the folder
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