I needed an encoder-service waiting to handle ffmpeg-workloads, and decided to use systemctl and a fifo pipe, so jobs could be queued without the need of RabbitMQ/other.

I'm aware of DLQ and fancy scaling, however this does the trick and hasn't failed for years.

1) Create script for initiating the fifo pipe, save it at /opt/createWorkerPipe.sh:

#!/bin/bash
# pipe location
pipe=/tmp/ffmpeg-pipe

trap "rm -f $pipe" EXIT

# Initiate pipe
[[ -p $pipe ]] || mkfifo $pipe

while true; do
    exec 3<> $pipe
    read line < $pipe
    bash <<< "/opt/ffmpeg-worker.sh $line"
done

2) Create your ffmpeg-worker, with your ffmpeg args, at /opt/ffmpeg-worker.sh:

#!/bin/bash 
# Do ffmpeg stuff
/usr/bin/ffmpeg -y input.avi [yourargs] output.mp4

3) Create service file at /etc/systemd/system/ffmpeg-encoder.service:

[Unit]
Description=ffmpeg encoder service
DefaultDependencies=no
After=network.target

[Service]
Type=simple
User=www-data
Group=www-data
ExecStart=/opt/createWorkerPipe.sh:
TimeoutStartSec=0
RemainAfterExit=yes

[Install]
WantedBy=default.target

3) Reload systemctl daemon: systemctl daemon-reload

4) Enable service: systemctl enable ffmpeg-encoder.service

Verify the service state with: systemctl status ffmpeg-encoder.service

Verifying service status programatially can be done by running:

systemctl is-active --quiet ffmpeg-encoder.service

where exitcode 0 is the active state of the service.

I also wrote a simple ffmpeg-log-parser for polling state via PHP, but that's for another post.