[LV2] Midi output using atomport

Lucas Takejame lucas at takejame.com.br
Fri Apr 4 13:07:58 PDT 2014

That was the problem, the output atom should be sequence, now its working!
Thanks =)

2014-04-04 14:36 GMT-03:00 David Robillard <d at drobilla.net>:

> On Thu, 2014-04-03 at 20:11 -0300, Lucas Takejame wrote:
> > Hello everybody, Im trying to make a lv2 plugin that translate audio to
> > MIDI, im using Aubio lib and Im having trouble to send the MIDI output. I
> > already saw a bunch of lv2 examples, like fifths, sampler and gxtuner but
> > couldn't solve my problem... I'm confuse about the steps i should follow
> to
> > prepare my LV2_Atom_Sequence struct to output. Here's what i did until
> now
> > (This is not the actual code, I modified it to give a context, tried to
> put
> > only things related to the midi output port):
> Your best bet is to literally copy from these examples, that's what they
> are for.
> >     Note2midi *plugin = new Note2midi();
> >     plugin->out = new LV2_Atom_Sequence();
> Oh my.  Atoms are C structs, not C++ objects, allocation does not work
> this way.  LV2_Atom_Sequence is just a header, it is not large enough to
> actually contain any data.  I suggest testing with valgrind to find
> memory errors.
> In any case, outputs are allocated by the *host*, not the plugin, so
> this is probably just being overwritten anyway.
> > plugin->out->atom.type = plugin->midi_event;
> >     plugin->out->atom.size = sizeof(plugin->note.msg);
> This is incorrect, the output atom is a Sequence, not a MidiEvent.  This
> is probably your real problem.  Set the type to atom:Sequence, and leave
> the clearing to lv2_atom_sequence_clear.  Both of these things need to
> be done in run() every cycle, not just once at startup.
> Assuming you are okay with using the new utility functions like
> lv2_atom_sequence_clear (which you're already doing, so I assume you
> are), you should just do exactly what fifths does to set up its output
> buffer, except instead of being able to simply copy the type from the
> input, if you don't have a MIDI input you'll have to map atom:Sequence
> and set it to that instead of in_port->atom.type
> > Hope this is not asking too much =)
> That's what the list is here for :)
> --
> dr

Lucas Conejero Takejame
Engenharia Elétrica - ênfase em computação
Escola Politécnica - USP
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