Rtsp to mjpeg using a router?

Question

Video

Hello.
There is a Chinese DVR that only streams via rtsp. There was a need to receive a stream in mjpeg.
Google says that everything is perfectly done by means of ffmpeg (ffserver).
There is a mikrotik router available on which you can easily install openWRT as a metarouter. But the problem is that I can’t find ffserver on openWRT ..
Can anyone tell me what other options there are to recode the stream?