On 3/5/18 23:24, Borja Marcos wrote:

> That would be really awesome, defining some standard “audio bus” for 
> radio applications.

Well, there's really not much to define since the work has already been
done for us by the IETF (Internet Engineering Task Force). Multicasting
is heavily used on LANs, mainly for resource discovery (especially by
Apple's Bonjour, which is also an IETF standard).

But IMHO IP multicasting hasn't lived up to its full potential, mainly
because few ISPs support it natively so you have to set up ad-hoc
tunnels. It's the basis of AT&T's U-verse service, and I'm looking hard
at using it for "smart" wide area roundtables and repeater links in ham
radio, but that's getting off topic.

RTP can be used with any audio format (or video, for that matter). I use
Opus (a fairly new and very nice lossy audio compression format) for
stuff I'm going to listen to by ear, but I still use PCM for anything
I'm going to feed to a demodulator program. They can easily coexist in
the same network. E.g., I wrote a simple server task that 'bridges'
multicast PCM to Opus to make it easy to listen remotely to the output
of a receiver module that produces only PCM.

> Making it multi platform and multi tooklit can be 
> tricky, though. WSJT-X is based on Qt audio. But, what about other apps?

The whole idea is to completely AVOID the audio subsystem on the host
computer running WSJT-X (or any other demod program, for that matter).
So there's no need for audio patching utilities like Jack or
Soundflower. A program like WSJT-X simply reads and processes (and/or
writes) multicast streams that just happen to contain digital audio. But
they're handled as ordinary data packets by the operating system.

But if I want to monitor the audio input to (or output from) a program
like WSJT-X, I can simply fire up a completely independent "multicast
monitor" program that joins the appropriate multicast group and streams
the audio to the local sound system. Otherwise I could listen to music,
watch a video, whatever, while WSJT-X quietly runs in its own window.


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