On Wed, Dec 28, 2011 at 1:46 PM, Iain Duncan <iainduncanlists@gmail.com> wrote:
> Hey folks, what is the easiest way to deal with midi input in a jack app?
> I'm confused by the difference in jack midi and alsa midi, because I have
> two midi inputs, one is a usb input, so it appears at a low level as an alsa
> device, but the other is the midi input on a firewire unit, and it appears
> as a jack midi device. I'd like to make sure that whatever I do is easy to
> port to other systems. Does it make sense to use portmidi or rtmidi to get
> input or should I stick to the jack api entirely?

JACK's MIDI API is substantially different from all others in that you
receive MIDI data in the same thread (and same callback) that you
receive audio data. In this sense its much more like the APIs used by
plugin APIs to retrieve MIDI for use during the plugin API's
equivalent of JACK's process() call.

None of the other APIs that you've mentioned have this property, and
nor do any of the Windows MIDI APIs or CoreMIDI.

this means that you face opposing issues depending on which API you
choose to use:

 * if you use JACK:
       - MIDI data is trivially available to alter synthesis done
during process()
       - MIDI data needs to be moved across thread boundaries to be
useful outside of process()

 * if you use ALSA, portmidi, rtmidi, CoreMIDI or anything else
      - MIDI data to be used for synthesis has to be moved across
thread boundaries
      - MIDI data used for other purposes can often be used in the
same thread it was received in,
                though not always.

this issue is far more substantive than the question of whether you
can access a firewire-based MIDI port or a USB-based MIDI port.

--p