1. Find the cache file for chrome you could find the place: C:\Users\Uname\AppData\Local\Google\Chrome\User Data\Default\Cache since it is invisible, you can go IE choose Tools->Internet options->Browsing history ->settings open the file fold, than find fold according to address above.
2. According to time, size etc. find the right file you think. Then copy to another place, rename it with FLV，F4V, Mp4.
Now, you download the file.