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Python MIDI IO
The Python MIDI IO module provides a domain model for midi events and supports reading and write from standard midi files.
Features
- High level class types that represent individual MIDI events.
- A multi-track aware container, that allows you to manage your MIDI events.
- A reader and writer, so you can read and write your MIDI tracks to disk.
Installation
First, make sure you have swig installed (www.swig.org)
Follow the normal procedure for Python module installation:
python setup.py install
Examine a MIDI File
To examine the contents of a MIDI file run
$ mididump.py mary.mid
This will print out a representation of "Mary had a Little Lamb" as executable python code.
Example Usage
Building a MIDI File from scratch
It is easy to build a MIDI track from scratch.
import midi
# Instantiate a MIDI note on event, append it to the track
on = midiio.NoteOnEvent(tick=0, velocity=20, pitch=midiio.G_3)
track.append(on)
# Instantiate a MIDI note off event, append it to the track
off = midiio.NoteOffEvent(tick=100, pitch=midiio.G_3)
track.append(off)
# Add the end of track event, append it to the track
eot = midiio.EndOfTrackEvent(tick=1)
# Instantiate a MIDI Track (contains a list of MIDI events)
track = midiio.Track((on, off, eot))
# Instantiate a MIDI Pattern (contains a list of tracks)
pattern = midiio.Pattern((track,))
# Print out the pattern
print pattern
# Save the pattern to disk
midiio.write_midifile("example.mid", pattern)
A MIDI file is represented as a hierarchical set of objects. At the top is a Pattern, which contains a list of Tracks, and a Track is is a list of MIDI Events.
The MIDI Pattern supports append(), extend(), slicing, and iteration. Patterns also contain global MIDI metadata: the resolution and MIDI Format.
The MIDI Track class does not have any special metadata like Pattern, but it does provide a few helper functions to manipulate all events within a track.
There are 27 different MIDI Events supported. In this example, three different MIDI events are created and added to the MIDI Track:
The NoteOnEvent captures the start of note, like a piano player pushing down on a piano key. The tick is when this event occurred, the pitch is the note value of the key pressed, and the velocity represents how hard the key was pressed.
The NoteOffEvent captures the end of note, just like a piano player removing her finger from a depressed piano key. Once again, the tick is when this event occurred, the pitch is the note that is released, and the velocity has no real world analogy and is usually ignored. NoteOnEvents with a velocity of zero are equivalent to NoteOffEvents.
The EndOfTrackEvent is a special event, and is used to indicate to MIDI sequencing software when the song ends. With creating Patterns with multiple Tracks, you only need one EndOfTrack event for the entire song. Most MIDI software will refuse to load a MIDI file if it does not contain an EndOfTrack event.
You might notice that the EndOfTrackEvent has a tick value of 1. This is because MIDI represents ticks in relative time. The actual tick offset of the MidiTrackEvent is the sum of its tick and all the ticks from previous events. In this example, the EndOfTrackEvent would occur at tick 101 (0 + 100 + 1).
Side Note: What is a MIDI Tick?
The problem with ticks is that they don't give you any information about when they occur without knowing two other pieces of information, the resolution, and the tempo. The code handles these issues for you so all you have to do is think about things in terms of milliseconds, or ticks, if you care about the beat.
A tick represents the lowest level resolution of a MIDI track. Tempo is always analogous with Beats per Minute (BPM) which is the same thing as Quarter notes per Minute (QPM). The Resolution is also known as the Pulses per Quarter note (PPQ). It analogous to Ticks per Beat (TPB).
Tempo is set by two things. First, a saved MIDI file encodes an initial Resolution and Tempo. You use these values to initialize the sequencer timer. The Resolution should be considered static to a track, as well as the sequencer. During MIDI playback, the MIDI file may have encoded sequenced (that is, timed) Tempo change events. These events will modulate the Tempo at the time they specify. The Resolution, however, can not change from its initial value during playback.
Under the hood, MIDI represents Tempo in microseconds. In other words, you convert Tempo to Microseconds per Beat. If the Tempo was 120 BPM, the python code to convert to microseconds looks like this:
>>> 60 * 1000000 / 120 500000
This says the Tempo is 500,000 microseconds per beat. This, in combination with the Resolution, will allow you to convert ticks to time. If there are 500,000 microseconds per beat, and if the Resolution is 1,000 than one tick is how much time?
>>> 500000 / 1000 500 >>> 500 / 1000000.0 0.00050000000000000001
In other words, one tick represents .0005 seconds of time or half a millisecond. Increase the Resolution and this number gets smaller, the inverse as the resolution gets smaller. Same for Tempo.
Although MIDI encodes Time Signatures, it has no impact on the Tempo. However, here is a quick refresher on Time Signatures:
http://en.wikipedia.org/wiki/Time_signature
Reading our Track back from Disk
It's just as easy to load your MIDI file from disk.
import midiio
pattern = midiio.read_midifile("example.mid")
print pattern
History
This module is based on a fork of the [python-midi](https://github.com/vishnubob/python-midi) and was started because the lacking Python 3 support. From the original module support for sequencing midi events was removed and it was slightly restructured.
