user20175: 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.

user11523: 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"


user14504: Always. As does Vimeo. 
You can as the publisher still access the original upload. That file is retained on youtube’s server. 
But even when posting 1080, the public 1080 is a re-encode from your upload. 

20175: <p>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).</p>

<p>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?</p>

<p>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.</p>
 11523: <p>Yes, youtube re-encode videos. You can see more information <a href="https://support.google.com/youtube/answer/1722171?hl=en" rel="nofollow noreferrer">here</a>, and find, which codecs most fits for youtube upload (in case you will make new ones).</p>

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

<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/8qKz5YW5J-U?start=0"></iframe>
            </div></div></p>

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

<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/r6Rp-uo6HmI?start=153"></iframe>
            </div></div></p>

<p>About "When": Re-encoding happens right after uploading in the save progress-bar will be written "Processing"
<a href="https://i.stack.imgur.com/ePhZY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ePhZY.png" alt="enter image description here"></a></p>
 14504: <p>Always. As does Vimeo. </p>

<p>You can as the publisher still access the original upload. That file is retained on youtube’s server. </p>

<p>But even when posting 1080, the public 1080 is a re-encode from your upload. </p>
