Your streams are offline now but the correct command should be
Code:
rtmpdump.exe -r "rtmp://68.68.29.10:1935/live/_definst_/mnbbmnmnmnbnbmmnb" --live --quiet | "C:\Program Files\VideoLAN\VLC\vlc.exe" -
replace the rtmp url with working one and also make sure that your vlc.exe path is correct.