[LAD] making sense of Jack MIDI; or, is this an appropriate use for Jack?

Paul Davis paul at linuxaudiosystems.com
Fri Feb 15 16:12:04 UTC 2013

On Fri, Feb 15, 2013 at 11:23 AM, M Donalies <ingeniousnebbish at cox.net>wrote:

> From what I can tell, the Jack midi interface aspires to hide the
> underlying
> Alsa api so an app developer can just use Jack midi and not have to muck
> with
> Asla.

that is a part of the goal, but a deeper one is to provide sample-accurate
and zero-copy delivery of MIDI between JACK clients, with data arriving in
the context of the process() callback where it can be used for synthesis
and control without crossing thread boundaries.

> If this is true, then how do I use Jack in the following senerio: I'm
> writing
> a toy gui SMF player that outputs midi events so a program like fluidsynth
> can
> play them.
> Using Alsa sequencer, I put events on a queue with a time and Alsa takes
> care
> of the rest. If I just use the Jack midi api, how much of this process can
> Jack do? I'm assuming "not much," since all the apps that I've looked at
> the
> source of use the Alsa sequencer.

JACK does not provide sequencing facilities. It simply transports MIDI
between ports.

> If I wanted to do the sequencing myself, what would be involved?

a lot.

Or am I
> completely missing the point of what Jack can do?

you seem to understand it reasonably well.

> --
> 7:8
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