How to remove FFMPEG delay when capturing 1 frame?

Question

RTMP

You need to take a snapshot from the RTMP stream.
I do this with the command:
ffmpeg -i rtmp://195.191.182.6/small/cam4 -vframes 1 -an -y -s 854x480 -f image2 tmp.jpg
Snapshot is created, but the problem is that FFMPEG takes up to 30 seconds to think . before he finishes the job.
How to speed up this process or are there other alternatives?