How to terminate a downloading task when rtmpdump.exe is still on?

[general]

Hello everyone,

Short description: During a downloading session, get_iplayer, after 
calling rtmpdump.exe, can not response to user input like Ctrl+c to 
terminate the program. It happens also when ffmpeg is being called to 
convert a downloaded flv file. Normally ffmpeg can be terminated by 
Ctrl+c when it is called in cmd.exe. So I guess the application response 
priority has been changed in get_iplayer script written in perl.

How can I terminate rtmpdump.exe when it is still on?

Long description:
Due to my slow and unreliable  internet, sometimes an unfinished task 
has to be resumed. The rtmpdump.exe can not response at all during 
normal downloading state unless when it stops and  resumes the task by 
itself, pressing Ctrl+c just at that moment can terminate the current 
task. After that, it is always successful to resume the unfinished task 
by get_iplayer.

However, rtmpdump.exe may not stop a task on a very bad internet 
connection, instead it prints repeatedly some unhopeful information like:
   WARNING: HandleInvoke, Sanity failed. no string method in invoke packet

Under such situation rtmpdump.exe can not response at all. It has to be 
killed, but unfortunately when it is called again by get_iplayer, it can 
not resume but prints:
     ERROR: Last tag size must be greater/equal zero 
(prevTagSize=1978859951) and smaller then filesize, corrupt file!

I have to use a php script "flvfixer" to recover the corrupted file so 
the file can be downloaded again.

Thanks a lot,
Zhe