So i came across this handy scripts.

As part of some new offensive ;), or maybe just privacy concerns for the user.
Flash now right after beginning a FLV download
deletes the file from the /tmp directory

As it still has a lock on the file descriptor, it disappears right after the flash player closes.

Let the video finish streaming and then run this script
It will save the deleted flv videos with open file descriptors into the folder where you have run the script.