Hi!
I believe this problem has not been addressed here, yet.
Since yesterday, at least that I've noticed, some videos from VEVO on Youtube can not be downloaded by the usual methods.
For example, this one ->
http://www.youtube.com/watch?v=E0oyglKjbFQ
Neither VideoDownloadHelper (Firefox extension) or web sites as KeepVid/SnipMp3 can capture that media stream.
I tried using rtmpdump (binaries compiled by KSV), but rtmpsrv/rtmpsuck not detect anything.
Maybe somebody smarter than I can find what is happening here and, hopefully, share a workaround...