We are streaming to flash and STBs. Feeds are encoded into h264/aac, pushed into Wowza by UDP and broadcasted by RTMP. We get artifacts on the screen, once in 5-10 minutes, mostly on static parts of the picture (lots of squares, wrong colors).
The same feed being received by VLC on the same server from the same UDP source is fine, no pixelization.
Wowza does not do any transcoding, only restreaming.
Issue is not related to a number of clients connected, glitches either with one and with few hundred watching the stream. Same behavior on four different Wowza servers.