rtmpdump as images

rtmpdump as images

 

Do you know how to save live stream as images
it's suppose to be somthing like this
rtmpdump -r "rtmp://myDomain/live/ff" -v live -o image%d.jpg
but it didnt work also i trued with ffmpeg and get rtmp error
if i convert the live stream to flv it's work fine
thanks