[Woebegone]

I use Cygwin as well. I often have multiple streams running, so "ps" doesn't do it for me. I found the following command allows me to pick the right rtmpdump stream to kill:

WMIC.exe PROCESS get CommandLine,ProcessId

I parse out the lines and grep the particular stream I want dead. Then kill -9 on the correct pid works pretty well for me. The only downside is the (partial) stream doesn't get finished, so stream viewers will think it's a live stream. I'm sure a quick trip through ffmpeg would clear that up, though. (I haven't actually tried, cause I throw away the streams I kill.)