We are trying to use zmqsend (it's part of the ffmpeg repository) to communicate with a ffmpeg instance. On Raspbian, ffmpeg is configured with --enable-libzmq, and libzmq-dev is installed, but zmqsend is not found. How to get it, besides by rebuilding ffmpeg?
Zmqsend can indeed be compiled independently. You need libzmq3-dev (not libzmq-dev) and libavutil-dev.
cd FFmpeg/ ./configure cd tools/ gcc -o /where/you/want/zmqsend zmqsend.c -I.. `pkg-config --libs --cflags libzmq libavutil`