Program arguments from payload

[nagyrobi]

Hi @jpmens thanks for this great experiment!

I was thinking to implement a simple mqtt media player on linux which could be use to play TTS messages from Home Assistant.
It's very simple, HA renders the TTS stream as an MP3 available on its own server via http protocol, so something like
mplayer -volume 80 http://home.assistant.address:8123/api/tts_proxy/6a0efdf280bf8c79a.mp3
shot from the command line would play the sound.

The goal is to be able to get the URL from the payload because that changes every time, at every message spoken.
So with mqtt-launcher we would need a variable containing the payload to be accessed in the program & arguments part of the config. For example sending the URL above to the topic mybox/mediaplay could be decoded with a special key like @payload@:

# topic         payload value           program & arguments
"mybox/mediaplay"  :   {
                    '@payload@'        :   [ 'mplayer', '-volume', '80', '@payload@'],
                },

Or anything similar...
What do you think?

[jpmens]

Related to #35

[hurra]

A solution with regular expressions and capture groups ist the most flexible here

[amotl]

Dear @nagyrobi, @hurra, and @toblie,

thanks a stack for sharing your use cases. We added a corresponding implementation to the mqttwarn example gallery at Simple MQTT media player with mqttwarn and mplayer. Enjoy, and let us know about any issues or success stories over at the mqttwarn issue tracker.

With kind regards,
Andreas.