Replay Media Catcher works fine for me for recording RTMP streams from arte.tv like
Code:
http://liveweb.arte.tv/fr/video/Christophe__en_direct_de_la_Cite_de_la_Musique
RMC is a Windows software, but it can be used on a Mac with freeware Wine:
How to install and run Replay Media Catcher on Mac OS X (Snow Leopard)