Standard MIDI file, typically known just as "MID", is a standard way to serialize series of MIDI events, which is a protocol used in many music synthesizers to transfer music data: notes being played, effects being applied, etc.
Internally, file consists of a header and series of tracks, every track listing MIDI events with certain header designating time these events are happening.
NOTE: Rarely, MIDI files employ certain stateful compression scheme to avoid storing certain elements of further elements, instead reusing them from events which happened earlier in the stream. Kaitai Struct (as of v0.9) is currently unable to parse these, but files employing this mechanism are relatively rare.
This page hosts a formal specification of Standard MIDI file using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for Ruby generated by Kaitai Struct depends on the Ruby runtime library. You have to install it before you can parse data.
The Ruby runtime library can be installed from RubyGems:
gem install kaitai-structParse a local file and get structure in memory:
data = StandardMidiFile.from_file("path/to/local/file.mid")
Or parse structure from a string of bytes:
bytes = "\x00\x01\x02..."
data = StandardMidiFile.new(Kaitai::Struct::Stream.new(bytes))
After that, one can get various attributes from the structure by invoking getter methods like:
data.hdr # => get hdr
# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
require 'kaitai/struct/struct'
unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.9')
raise "Incompatible Kaitai Struct Ruby API: 0.9 or later is required, but you have #{Kaitai::Struct::VERSION}"
end
##
# Standard MIDI file, typically known just as "MID", is a standard way
# to serialize series of MIDI events, which is a protocol used in many
# music synthesizers to transfer music data: notes being played,
# effects being applied, etc.
#
# Internally, file consists of a header and series of tracks, every
# track listing MIDI events with certain header designating time these
# events are happening.
#
# NOTE: Rarely, MIDI files employ certain stateful compression scheme
# to avoid storing certain elements of further elements, instead
# reusing them from events which happened earlier in the
# stream. Kaitai Struct (as of v0.9) is currently unable to parse
# these, but files employing this mechanism are relatively rare.
class StandardMidiFile < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@hdr = Header.new(@_io, self, @_root)
@tracks = []
(hdr.num_tracks).times { |i|
@tracks << Track.new(@_io, self, @_root)
}
self
end
class TrackEvents < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@event = []
i = 0
while not @_io.eof?
@event << TrackEvent.new(@_io, self, @_root)
i += 1
end
self
end
attr_reader :event
end
class TrackEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@v_time = VlqBase128Be.new(@_io)
@event_header = @_io.read_u1
if event_header == 255
@meta_event_body = MetaEventBody.new(@_io, self, @_root)
end
if event_header == 240
@sysex_body = SysexEventBody.new(@_io, self, @_root)
end
case event_type
when 224
@event_body = PitchBendEvent.new(@_io, self, @_root)
when 144
@event_body = NoteOnEvent.new(@_io, self, @_root)
when 208
@event_body = ChannelPressureEvent.new(@_io, self, @_root)
when 192
@event_body = ProgramChangeEvent.new(@_io, self, @_root)
when 160
@event_body = PolyphonicPressureEvent.new(@_io, self, @_root)
when 176
@event_body = ControllerEvent.new(@_io, self, @_root)
when 128
@event_body = NoteOffEvent.new(@_io, self, @_root)
end
self
end
def event_type
return @event_type unless @event_type.nil?
@event_type = (event_header & 240)
@event_type
end
def channel
return @channel unless @channel.nil?
if event_type != 240
@channel = (event_header & 15)
end
@channel
end
attr_reader :v_time
attr_reader :event_header
attr_reader :meta_event_body
attr_reader :sysex_body
attr_reader :event_body
end
class PitchBendEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@b1 = @_io.read_u1
@b2 = @_io.read_u1
self
end
def bend_value
return @bend_value unless @bend_value.nil?
@bend_value = (((b2 << 7) + b1) - 16384)
@bend_value
end
def adj_bend_value
return @adj_bend_value unless @adj_bend_value.nil?
@adj_bend_value = (bend_value - 16384)
@adj_bend_value
end
attr_reader :b1
attr_reader :b2
end
class ProgramChangeEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@program = @_io.read_u1
self
end
attr_reader :program
end
class NoteOnEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@note = @_io.read_u1
@velocity = @_io.read_u1
self
end
attr_reader :note
attr_reader :velocity
end
class PolyphonicPressureEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@note = @_io.read_u1
@pressure = @_io.read_u1
self
end
attr_reader :note
attr_reader :pressure
end
class Track < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@magic = @_io.read_bytes(4)
raise Kaitai::Struct::ValidationNotEqualError.new([77, 84, 114, 107].pack('C*'), magic, _io, "/types/track/seq/0") if not magic == [77, 84, 114, 107].pack('C*')
@len_events = @_io.read_u4be
@_raw_events = @_io.read_bytes(len_events)
_io__raw_events = Kaitai::Struct::Stream.new(@_raw_events)
@events = TrackEvents.new(_io__raw_events, self, @_root)
self
end
attr_reader :magic
attr_reader :len_events
attr_reader :events
attr_reader :_raw_events
end
class MetaEventBody < Kaitai::Struct::Struct
META_TYPE_ENUM = {
0 => :meta_type_enum_sequence_number,
1 => :meta_type_enum_text_event,
2 => :meta_type_enum_copyright,
3 => :meta_type_enum_sequence_track_name,
4 => :meta_type_enum_instrument_name,
5 => :meta_type_enum_lyric_text,
6 => :meta_type_enum_marker_text,
7 => :meta_type_enum_cue_point,
32 => :meta_type_enum_midi_channel_prefix_assignment,
47 => :meta_type_enum_end_of_track,
81 => :meta_type_enum_tempo,
84 => :meta_type_enum_smpte_offset,
88 => :meta_type_enum_time_signature,
89 => :meta_type_enum_key_signature,
127 => :meta_type_enum_sequencer_specific_event,
}
I__META_TYPE_ENUM = META_TYPE_ENUM.invert
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@meta_type = Kaitai::Struct::Stream::resolve_enum(META_TYPE_ENUM, @_io.read_u1)
@len = VlqBase128Be.new(@_io)
@body = @_io.read_bytes(len.value)
self
end
attr_reader :meta_type
attr_reader :len
attr_reader :body
end
class ControllerEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@controller = @_io.read_u1
@value = @_io.read_u1
self
end
attr_reader :controller
attr_reader :value
end
class Header < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@magic = @_io.read_bytes(4)
raise Kaitai::Struct::ValidationNotEqualError.new([77, 84, 104, 100].pack('C*'), magic, _io, "/types/header/seq/0") if not magic == [77, 84, 104, 100].pack('C*')
@len_header = @_io.read_u4be
@format = @_io.read_u2be
@num_tracks = @_io.read_u2be
@division = @_io.read_s2be
self
end
attr_reader :magic
attr_reader :len_header
attr_reader :format
attr_reader :num_tracks
attr_reader :division
end
class SysexEventBody < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@len = VlqBase128Be.new(@_io)
@data = @_io.read_bytes(len.value)
self
end
attr_reader :len
attr_reader :data
end
class NoteOffEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@note = @_io.read_u1
@velocity = @_io.read_u1
self
end
attr_reader :note
attr_reader :velocity
end
class ChannelPressureEvent < Kaitai::Struct::Struct
def initialize(_io, _parent = nil, _root = self)
super(_io, _parent, _root)
_read
end
def _read
@pressure = @_io.read_u1
self
end
attr_reader :pressure
end
attr_reader :hdr
attr_reader :tracks
end