[Note: This README is currently a slightly mutated copy of https://github.com/jimm/midilib/blob/master/README.rdoc, so don't pay too much attention to it yet.]
Midifile is a library useful for reading and writing standard type 1 MIDI files and manipulating MIDI event data.
The GitHub project page and Web site of Midifile is http://github.com/jimm/elixir-midifile and the Hex page is https://hex.pm/packages/midifile.
TODO
% mix test
runs all of the tests in the test directory.
The Midifile MIDI file reader only understands MIDI file format 1, where a sequence is made up of multiple tracks. It doesn't yet understand format 0 (a single track containing all events) or format 2 (a collection of format 0 files in one file).
A sequence contains a list of tracks and global information like the sequence's format (always 1 for Midifile) and time division.
The first track in a sequence is special; it holds meta-events like tempo
and sequence name. It is stored as a sequence's conductor_track. Don't put
any notes in this track.
Midifile.Sequence also contains some convenience methods that let you [set
and] retrieve the sequence's name, [the time signature, and to retrieve the
first tempo event's beats-per-minute value].
A track contains an array of events.
When you modify the events array, make sure to call recalc_times so each
event gets its time_from_start recalculated. You don't have to do that
after every event you add; just remember to do so before using the track in
a way that expects the list of events to be ordered correctly.
A Track also holds a bit mask that specifies the channels used by the track. This bit mask is set when the track is read from the MIDI file by a SeqReader but is not kept up to date by any other methods. Specifically, if you add events to a track at any other time, the bit mask will not be updated.
This class contains information about a measure from the sequence. Measure data is based on the time signature information from the sequence and is not stored in the sequence itself.
The class Midifile.Sequence method get_measures returns a Midifile.Measures object. Midifile.Measures is a subclass of Array. It is a specialized container for Midifile.Measure objects, which can be use to map event times to measure numbers. Please note that this object has to be remade when events are deleted/added in the sequence.
Midifile.Measure and Midifile.Measures are brought to us by Jari Williamsson jari.williamsson@mailbox.swipnet.se, who also contributed some improvements to the Midifile.Event and Midifile.Track classes.
Each event holds not only its delta time but also its time from the start of the track. The track is responsible for recalculating its events' start times. You can call Midifile.Track#recalc_times to do so.
Subclasses of Midifile.Event implement the various MIDI messages such as note on and off, controller values, system exclusive data, and realtime bytes.
Midifile.Realtime events have delta values and start times, just like all the other Midifile event types do. (MIDI real time status bytes don't have delta times, but this way we can record when in a track the realtime byte was received and should be sent. This is useful for start/continue/stop events that control other devices, for example.) Note that when a Midifile.Realtime event is written out to a MIDI file, the delta time is not written.
Midifile.MetaEvent events hold an array of bytes named 'data'. Many meta events are string holders (text, lyric, marker, etc.) Though the 'data' value is always an array of bytes, Midifile.MetaEvent helps with saving and accessing string. The Midifile.MetaEvent#data_as_str method returns the data bytes as a string. When assigning to a meta event's data, if you pass in a string it will get converted to an array of bytes.
The following examples show you how to use Midifile to read, write, and manipulate MIDI files and modify track events. See also the files in the examples directory, which are described below.
To read a MIDI file, create a Midifile.Sequence object and call its #read method, passing in an IO object.
The #read method takes an optional block. If present, the block is called once after each track has finished being read. Each time, it is passed the track object, the total number of tracks and the number of the current track that has just been read. This is useful for notifying the user of progress, for example by updating a GUI progress bar.
require 'Midifile/io/seqreader'
seq = Midifile.Sequence.new()
File.open('my_midi_file.mid', 'rb') { | file | seq.read(file) { | track, num_tracks, i | # Print something when each track is read. puts "read track #{i} of #{num_tracks}" } }
To write a MIDI file, call the write method, passing in an IO object.
require 'Midifile/io/seqwriter'
seq = read_or_create_seq_we_care_not_how()
File.open('my_output_file.mid', 'wb') { | file | seq.write(file) }
Combining the last two examples, here is a script that reads a MIDI file, transposes some events, and writes the sequence out to a different file. This is a useful template for programatically manipulating MIDI data.
This code transposes all of the note events (note on, note off, and poly pressure) on channel 5 down one octave.
require 'Midifile/io/seqreader' require 'Midifile/io/seqwriter'
seq = Midifile.Sequence.new()
File.open('my_input_file.mid', 'rb') { | file | seq.read(file) { | track, num_tracks, i | # Print something when each track is read. puts "read track #{i} of #{num_tracks}" } }
seq.each { | track | track.each { | event | # If the event is a note event (note on, note off, or poly # pressure) and it is on MIDI channel 5 (channels start at # 0, so we use 4), then transpose the event down one octave. if Midifile.NoteEvent === event && event.channel == 4 event.note -= 12 end } }
File.open('my_output_file.mid', 'wb') { | file | seq.write(file) }
If you modify a track's list of events directly, don't forget to call Midifile.Track#recalc_times when you are done.
track.events[42, 1] = array_of_events track.events << an_event track.merge(array_of_events) track.recalc_times
A few methods in Midifile.Sequence make it easier to calculate the delta times that represent note lengths. Midifile.Sequence#length_to_delta takes a note length (a multiple of a quarter note) and returns the delta time given the sequence's current ppqn (pulses per quarter note) setting. 1 is a quarter note, 1.0/32.0 is a 32nd note (use floating-point numbers to avoid integer rounding), 1.5 is a dotted quarter, etc. See the documentation for that method for more information.
Midifile.Sequence#note_to_length takes a note name and returns a length value (again, as a multiple of a quarter note). Legal note names are those found in Midifile.Sequence::NOTE_TO_LENGTH, and may begin with "dotted" and/or end with "triplet". For example, "whole", "sixteenth", "32nd", "quarter triplet", "dotted 16th", and "dotted 8th triplet" are all legal note names.
Finally, Midifile.Sequence#note_to_delta takes a note name and returns a delta time. It does this by calling note_to_length, then passing the result to length_to_delta.
Here are short descriptions of each of the examples found in the examples directory.
-
examples/from_scratch.rb shows you how to create a new sequence from scratch and save it to a MIDI file. It creates a file called 'from_scratch.mid'.
-
examples/seq2text.rb dumps a MIDI file as text. It reads in a sequence and uses the to_s method of each event.
-
examples/reader2text.rb dumps a MIDI file as text. It subclasses Midifile.SeqReader instead of creating a sequence containing tracks and events.
-
examples/transpose.rb transposes all note events (note on, note off, poly pressure) on a specified channel by a specified amount.
-
There is also one MIDI file, examples/NoFences.mid. It is a little pop ditty I wrote. The instruments in this file use General MIDI patch numbers and drum note assignments. Since I don't normally use GM patches, the sounds used here are at best approximations of the sounds I use.
A description of the MIDI file format can be found in a few places such as https://www.csie.ntu.edu.tw/~r92092/ref/midi/.
The MIDI message reference at http://www.jimmenard.com/midi_ref.html describes the format of MIDI commands.
-
Visit the forums, bug list, and mailing list pages at http://rubyforge.org/projects/Midifile
-
Send email to Jim Menard at mailto:jim@jimmenard.com
-
Ask on the ruby-talk mailing list
Author:: Jim Menard (mailto:jim@jimmenard.com) Copyright:: Copyright (c) 2015 Jim Menard License:: Distributed under the same license as Elixir: Apache v2.0.
Midifile is copyrighted free software by Jim Menard and is released under the same license as Elixir: Apache v2.0.
Midifile may be freely copied in its entirety providing this notice, all source code, all documentation, and all other files are included.
Midifile is Copyright (c) 2015 by Jim Menard.
This software is provided "as is" and without any express or implied warranties, including, without limitation, the implied warranties of merchantability and fitness for a particular purpose.