I'm trying to understand if trimming a video uploaded to YouTube affects the quality of the trimmed video. I read on one blog that the video is copied. Not sure if that means it is re-encoded or just some start and end points removed. Ideally, I'd like to maintain the original upload quality even after trimming. If YouTube degrades the video quality, I'd want to trim it beforehand. I enjoy YouTube's tools but not at the cost of degraded quality.
YouTube keeps the original file you uploaded to them and uses that when trimming the video. So it'll get indeed reencoded, but you won't really see a loss of quality if you have enough of a buffer in terms of bitrate (ie if you've used the recommended settings.)