Live data sending from MIC to speaker over MQTT

[Proxy Hossain]

Is it possible to send live data from one device MIC to another device speaker  over MQTT protocol ?

scenario is, 

 one user will speak in his mobile-1 MIC,  another user will hear mobile-1 data which user speaks in MIC  in his mobile-2 speaker .

if possible, how live data sending can be done over mqtt?

[Nicholas Humfrey]

Hello again Proxy,

This isn't a very typical application for MQTT but it should be
possible.


I think one of the biggest design considerations is the latency you are
aiming for.

- Professional audio systems using AES67 can have latencies as low as 1
millisecond
- Apple's HTTP Live Streaming protocol (used by broadcasters) has a
typical latency of 10 seconds

Wikipedia says:
"VoIP systems typically have a minimum of 20 ms inherent latency and
target 150 ms as a maximum latency for general consumer use."

https://en.wikipedia.org/wiki/Latency_(audio)

So you will need to record the audio in 20ms chunks (for example),
encode it to GSM (or some other codec), then send it over MQTT.


The GSM audio codec uses a Sample Rate of 8khz and a bitrate of 13
kbit/s.
A GSM audio frame is 160 samples long - 20ms of audio and around 33
bytes of data.
On top of that is the MQTT Publish packet headers, including the topic
name - this will increase the overall packet length and bitrate. You
could reduce this overhead by increasing the latency.


Is this for a personal experiment, or building a product that lots of
people will be using?

If you are aiming to build a Voice over IP type application, then you
might be better off looking at SIP/RTP for streaming live audio - this
is what most VoIP phones use.


nick.

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