A local MQTT broker is required, such as mosquitto. Tested and developed on Ubuntu 20.10.
Use -record to record stream from MQTT.
-url "ws://url:80/mqtt"
-topic "test/#"
-output "test" // Output file, where to save recording.
Use -send to send a recording to a local MQTT broker.
-input "test" // Input file, where to find a recodring to send.