54 lines
1.9 KiB
Lua
54 lines
1.9 KiB
Lua
ardour {
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["type"] = "session",
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name = "Rewrite Midi",
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license = "MIT",
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author = "Ardour Team",
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description = [[An example session script preprocesses midi buffers.]]
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}
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function factory ()
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-- this function is called in every process cycle, before processing
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return function (n_samples)
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_, t = Session:engine ():get_ports (ARDOUR.DataType.midi (), ARDOUR.PortList ())
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for p in t[2]:iter () do
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if not p:receives_input () then goto next end
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-- search-filter port
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if not p:name () == "MIDITrackName/midi_in 1" then
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goto next -- skip
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end
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-- ensure that the port is-a https://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:MidiPort
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assert (not p:to_midiport ():isnil ())
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-- https://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:MidiBuffer
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local mb = p:to_midiport ():get_midi_buffer (n_samples)
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-- When an I/O port is connected (source -> sink), the
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-- buffer is shared. The MidiBuffer is in fact the buffer
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-- from the backend. Changing events in this buffer affects
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-- all destinations that use this buffer as source.
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local events = mb:table() -- *copy* event list to a Lua table
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mb:silence (n_samples, 0) -- clear existing buffer
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-- now iterate over events that were in the buffer
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for _,e in pairs (events) do
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-- e is-a http://manual.ardour.org/lua-scripting/class_reference/#Evoral:Event
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if e:size () == 3 then
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-- found a 3 byte event
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local buffer = e:buffer():array()
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local ev_type = buffer[1] >> 4 -- get MIDI event type (upper 4 bits)
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if ev_type == 8 or ev_type == 9 then -- note on or note off event
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buffer[1] = (buffer[1] & 0xf0) + 2 -- change the MIDI channel to "2"
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buffer[3] = buffer[3] >> 1 -- reduce the velocity by half
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end
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end
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-- finally place the event back into the Port's MIDI buffers
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mb:push_event (e)
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end
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::next::
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end
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end
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end
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