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livetrax/share/scripts/_midi_rewrite.lua

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