It seems that YouTube is in the process of identifying clips that contain copyrighted music, and rather than simply remove the videos, the audio portion of the clip is being muted. When viewing such a clip, you’ll see this message below the video:
This video contains an audio track that has not been authorised by all copyright holders. The audio has been disabled.
On the one hand, this seems like a pretty decent compromise: the video is still available, and YouTube is, after all, a video site. But on the other hand, it seems like a real disservice to uploaders. I haven’t uploaded anything to YouTube in ages, so I don’t know if you get some kind of notice that your video has been muted.
It’s also unclear to me whether any use of a copyrighted song is muted, or just those uses that violate the notoriously hard-to-define “fair use”. The YouTube Copyright Tips page says only “Unfortunately we cannot make a determination whether your video qualifies as fair use.” You can’t blame them for erring on the side of caution, but it’s still kind of a bummer.
: a post on the YouTube blog adds a little explanation about this, indicating that uploaders can choose to swap audio tracks with ones that have already been cleared. That’s nice.