How can I find duplicate videos from a large set of videos of varying formats? After losing a backup device with a bunch of my original videos I've had to download a large number of them (~300) back from Youtube. The new downloads are a mix of MP4 and FLV, and the originals are a mix of almost any video format due to lots of experimenting. 

To make matters worse there's no clear cutoff for when my local copies disappeared; I've found a point in my youtube videos chonologically where I have some of the videos and I don't have others. I've been trying to manually weed out videos where I already have a copy, but with this many videos I'm sure I've missed some.

How can I effectively go through several hundred videos of different formats and weed out duplicates? The names will be similar but not identical. The formats may be different, and the file size may be different due to that (and or encoding differences). The file lengths should be the same, and visually the videos should be similar enough, but I'm not sure there's any tool to sort that out visually. 

Am I doomed to go through the list based on running time and manually look for duplicates or is there a better way?
I'd recommend a hybrid approach using both computers and people.


Bucket the videos by their length (round to the nearest second)
For each bucket, use ffmpeg to generate thumbnails at a predictable and uniform point in the videos (ex: a frame from 10 seconds into the video)
Look at the generated thumbnails in a grid (most OS's provide a nice thumbnail view) and scan for duplicates to remove.


You shouldn't have to do any programming to perform these steps, though creating the thumbnails on the command line with ffmpeg may take some finesse.  Good luck!