When does YouTube Reencode Videos? I've got some videos on Vimeo that I want move over to my new channel on YouTube. I can download what Vimeo lists as the 'Original' files, ~2GB H.264 MP4s (20-30mins).

Does YouTube re-encode regardless of the incoming format, or does it just re-mux? I don't want any more video degradation than necessary; I figure YT will re-encode to optimize for delivery to other resolutions / bit-rates, but if my original files are 720p, will they get re-encoded / go through another lossy pass when re-uploaded to YouTube?

And to be clear, these are all /my/ videos (I'm the creator on both channels), so not trying to move someone else's content.
Yes, youtube re-encode videos. You can see more information here, and find, which codecs most fits for youtube upload (in case you will make new ones).

As a example of degradation, here is video, which was re-uploaded to youtube 1000 times in 2010 year:


                
            

And with different content you will see more degradation. You can see it here  at 2:33::


                
            

About "When": Re-encoding happens right after uploading in the save progress-bar will be written "Processing"