If you can speak German, there are good video tutorials at sempervideo.de
http://www.sempervideo.de/?p=3751   ZDF Mediathek Stream speichern (Folge 2)
http://www.sempervideo.de/?p=3807   RTMPDUMP: Southpark rippen

An Example Video to dump.
http://www.zdf.de/ZDFmediathek/#/beitrag/video/790410/Abschied-von-Jacko-in-Los-Angeles/

Here are the Parameters
-o             the filename                                     -o "c:\zdf.mp4"
-r              the URL                                           -r rtmp://ondemand.flash.zdf.newmedia.nacamar.net/zdf/mp4:zdf/data/quicktime/zdf/09/07/090703_neubauer_h19_vh.mp4
--host        the hostname                                   --host ondemand.flash.zdf.newmedia.nacamar.net
--port        the Port Number (default 1935)            --port 1935
--protocol   Protokoll rtmp oder rtmpe (encrypted)   --protocol rtmp
--playpath   the playpath behind the first path        --playpath mp4:zdf/data/quicktime/zdf/09/07/090703_neubauer_h19_vh.mp4
--swfUrl      the swf-player                                  --swfUrl http://www.zdf.de/ZDFmediathek/flash/player.swf
--tcUrl        the first part of the rtmp-URL              --tcUrl rtmp://ondemand.flash.zdf.newmedia.nacamar.net/zdf
--pageUrl    URL from PopUp                                 --pageUrl http://www.zdf.de/ZDFmediathek/content/9602?inPopup=true
--app         the first path behind the host-url          --app zdf
--flashVer   which version of Flash ?                      --flashVer "WIN 10,0,22,87"
( --auth     don't know the use of Authentication )

There are several ways to use the parameters to dump the video
the complete with 10 parameters -o --host --port --protocol -playpath --swfUrl --tcUrl --pageUrl --app --flashVer
rtmpdump.exe -o "c:\zdf.mp4" --host ondemand.flash.zdf.newmedia.nacamar.net --port 1935 --protocol rtmp --playpath mp4:zdf/data/quicktime/zdf/09/07/090703_neubauer_h19_vh.mp4 --swfUrl http://www.zdf.de/ZDFmediathek/flash/player.swf --tcUrl rtmp://ondemand.flash.zdf.newmedia.nacamar.net/zdf --pageUrl http://www.zdf.de/ZDFmediathek/content/9602?inPopup=true --app zdf --flashVer "WIN 10,0,22,87"

or shorter with just 4 parameters -o --host --playpath --app
rtmpdump.exe -o "c:\zdf.mp4" --host ondemand.flash.zdf.newmedia.nacamar.net --playpath mp4:zdf/data/quicktime/zdf/09/07/090703_neubauer_h19_vh.mp4 --app zdf

with 3 parameters -o -r und --playpath
rtmpdump.exe -o "c:\zdf.mp4" -r rtmp://ondemand.flash.zdf.newmedia.nacamar.net/zdf/mp4:zdf/data/quicktime/zdf/09/07/090703_neubauer_h19_vh.mp4 --playpath mp4:zdf/data/quicktime/zdf/09/07/090703_neubauer_h19_vh.mp4

hope this helps