So you want to have play audio and video in reverse ? Is there a secret satanic message in it??
If I had to do such a thing... I'd do it this
Download the .flv vid from youtube, using a video download add on in firefox like download helper
Then just use the vlc player to play it backwards.
If you need to have it like that to be able to send out etc... Id use FRAPS to capture the VLC player playing (the audio and video) backwards
There is a youtube vid of just the audio backwards I noticed... if it is something important in having the video backwards, someone would have already done it surely