So I did post already the right minimum command line for you which you can use.So in your case....
Code:
rtmpdump_path_to_exe
--live|-v Save a live stream, no --resume (seeking) of live streams possible
--rtmp|-r url URL (e.g. rtmp://host[:port]/path)
--playpath|-y path Overrides the playpath parsed from rtmp url
--flv|-o string FLV output file name, if the file name is - print stream to stdout
or
| playerpath -
...just check the entire description of rtmpdump help.Also see on the board for postet rtmpdump links so there are tons of them etc.
PS: Yes there are some commands which you can use so in some other or special cases you need to use more.Just try it.
greetz