# "audio plugin host" MIDI Output **URL:** \ **Category:** General JUCE discussion\ **Created:** [December 2, 2014, 3:38am UTC](https://forum.juce.com/t/audio-plugin-host-midi-output/13964 "2014-12-02T03:38:20Z")\ **Posts on this page:** 1\ **Showing post:** 7
**Author:** ![mnsp](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/mnsp/32/2665_2.png) [@mnsp](https://forum.juce.com/u/mnsp)\ **Post date:** [September 20, 2019, 6:21am UTC](https://forum.juce.com/t/audio-plugin-host-midi-output/13964/7 "2019-09-20T06:21:04Z")
As promised, here are the [instructions originally posted by oxxyyd](https://forum.juce.com/t/processblock-and-midioutput/12060/17) on how to modify the plugin host to handle midi out, updated to JUCE version 5.4.4: 1 First you need to add some code to actually create the midi out connection so to say In InternalPlugins.h you change ``` PluginDescription audioInDesc, audioOutDesc, midiInDesc; ``` to ``` PluginDescription audioInDesc, audioOutDesc, midiInDesc, midiOutDesc; ``` in InternalPlugins.cpp you add in the relevant places: ``` { AudioProcessorGraph::AudioGraphIOProcessor p (AudioProcessorGraph::AudioGraphIOProcessor::midiOutputNode); p.fillInPluginDescription (midiOutDesc); } ``` and ``` if (name == midiOutDesc.name) return std::make_unique (AudioProcessorGraph::AudioGraphIOProcessor::midiOutputNode); ``` and ``` midiOutDesc, ``` to the line that says ``` results.add (audioInDesc, audioOutDesc, midiInDesc, ``` (hint: search for midiInDesc and add the corresponding code for midiOutDesc). In PluginGraph.cpp you add ``` addPlugin (internalFormat.midiOutDesc, { 0.25, 0.9 }); ``` NOTE: at this point your code should be in a state that will compile and the MIDI Output node should appear in the plugin graph (but it doesn’t work yet). 2 Some more updates Add to the collection of privates of GraphDocumentComponent in GraphEditorPanel.h ``` MidiOutput *midiOut; ``` Make GraphDocumentComponent a ChangeListener i.e in GraphEditorPanel.h it should look like ``` class GraphDocumentComponent : public Component, public DragAndDropTarget, public DragAndDropContainer, public ChangeListener ``` and add the following line to the public part of the class declaration: ``` void changeListenerCallback(ChangeBroadcaster* source) override; ``` 3 Add to GraphEditorPanel.cpp ``` void GraphDocumentComponent::changeListenerCallback(ChangeBroadcaster* source) { if (source == &deviceManager) { midiOut = deviceManager.getDefaultMidiOutput(); if (midiOut) { midiOut->startBackgroundThread(); } graphPlayer.setMidiOutput(midiOut); } } ``` 4 Now add the line ``` changeListenerCallback(&deviceManager); ``` somewhere in the constructor of GraphDocumentComponent (GraphEditorPanel.cpp). and put following at the to beginning of ~GraphDocumentComponent ``` if (midiOut) midiOut->stopBackgroundThread(); ``` and add to the method init(), after the line that begins with “keyState.addListener”, the line ``` deviceManager.addChangeListener(this); ``` 5 Now we’ve come to the part where midi output is actually taken from the AudioProcessorGraph. Modify the code below by adding the 7 lines after ``` // modification for MIDI output: ``` In juce\_AudioProcessorPlayer.cpp: ``` if (! processor->isSuspended()) { if (processor->isUsingDoublePrecision()) { conversionBuffer.makeCopyOf (buffer, true); processor->processBlock (conversionBuffer, incomingMidi); buffer.makeCopyOf (conversionBuffer, true); } else { processor->processBlock (buffer, incomingMidi); } // modification for MIDI output: AudioProcessorGraph* processorgraph=dynamic_cast(processor); if (processorgraph) { MidiBuffer* midiBuffer (processorgraph->getCurrentMidiOutputBuffer()); if (midiBuffer && !midiBuffer->isEmpty() && midiOutput) { midiOutput->sendBlockOfMessages(*midiBuffer, Time::getMillisecondCounter(), getCurrentProcessor()->getSampleRate()); } } return; } ``` 6 And last add following method declaration to the publics of juce\_AudioProcessorGraph.h ``` // modification for MIDI output: MidiBuffer* getCurrentMidiOutputBuffer(); ``` and the corresponding implementation in juce\_AudioProcessorGraph.cpp: ``` // modification for MIDI output: MidiBuffer* AudioProcessorGraph::getCurrentMidiOutputBuffer() { if (isUsingDoublePrecision()) { if (renderSequenceDouble != nullptr) { return &renderSequenceDouble->currentMidiOutputBuffer; } else { return nullptr; } } else { if (renderSequenceFloat != nullptr) { return &renderSequenceFloat->currentMidiOutputBuffer; } else { return nullptr; } } } ``` After building and starting the plugin host you should now have a MIDI output. Draw a connection between midi input and midi output. If you have selected a midiout device in the audiosettings (e.g Microsft GS Wavetable Synth in windows) you should now here a piano when playing on the midikeyboard (or see the MIDI Out LED blink if you selected a physical MIDI interface). Note from original instructions (which I would not necessarily recommend, especially if it involves copying and pasting a lot of JUCE library code, which then has to be maintained to keep track with the changes that are being made to JUCE), added here for the sake of completeness: > If you’re more into copy & paste programming you could instead of modifying the two [now three] juce files create a “midiout processor” by subclassing juce\_AudioProcessor. But I leave that as an excersise for the reader… --- _[View the full topic](https://forum.juce.com/t/audio-plugin-host-midi-output/13964)._