NAME

MIDI::Event - MIDI events

SYNOPSIS

  # Dump a MIDI file's text events
  die "No filename" unless @ARGV;
  use MIDI;  # which "use"s MIDI::Event;
  MIDI::Opus->new( {
     "from_file" => $ARGV[0],
     "exclusive_event_callback" => sub{print "$_[2]\n"},
     "include" => \@MIDI::Event::Text_events
   } ); # These options percolate down to MIDI::Event::decode
  exit;

DESCRIPTION

Functions and lists to do with MIDI events and MIDI event structures.

An event is a list, like:

  ( 'note_on', 141, 4, 50, 64 )

where the first element is the event name, the second is the delta-time, and the remainder are further parameters, per the event-format specifications below.

An event structure is a list of references to such events -- a "LoL". If you don't know how to deal with LoLs, you must read perllol.

GOODIES

For your use in code (as in the code in the Synopsis), this module provides a few lists:

@MIDI_events: a list of all "MIDI events" AKA voice events -- e.g., 'note_on'
@Text_events: a list of all text meta-events -- e.g., 'track_name'
@Nontext_meta_events: all other meta-events (plus 'raw_data' and F-series events like 'tune_request').
@Meta_events: the combination of Text_events and Nontext_meta_events.
@All_events: the combination of all the above lists.

FUNCTIONS

This module provides three functions of interest, which all act upon event structures. As an end user, you probably don't need to use any of these directly, but note that options you specify for MIDI::Opus->new with a from_file or from_handle options will percolate down to these functions; so you should understand the options for the first two of the below functions. (The casual user should merely skim this section.)

MIDI::Event::decode( \$data, { ...options... } ): This takes a reference to binary MIDI data and decodes it into a new event structure (a LoL), a reference to which is returned. Options are:

'include' => LISTREF: If specified, listref is interpreted as a reference to a list of event names (e.g., 'cue_point' or 'note_off') such that only these events will be parsed from the binary data provided. Events whose names are NOT in this list will be ignored -- i.e., they won't end up in the event structure, and they won't be each passed to any callbacks you may have specified.
'exclude' => LISTREF: If specified, listref is interpreted as a reference to a list of event names (e.g., 'cue_point' or 'note_off') that will NOT be parsed from the binary stream; they'll be ignored -- i.e., they won't end up in the event structure, and they won't be passed to any callbacks you may have specified. Don't specify both an include and an exclude list. And if you specify neither, all events will be decoded -- this is what you probably want most of the time. I've created this include/exclude functionality mainly so you can scan a file rather efficiently for just a few specific event types, e.g., just text events, or just sysexes.
'no_eot_magic' => 0 or 1: See the description of 'end_track', in "EVENTS", below.
'event_callback' => CODEREF: If defined, the code referred to (whether as "\&wanted" or as "sub { BLOCK }") is called on every event after it's been parsed into an event list (and any EOT magic performed), but before it's added to the event structure. So if you want to alter the event stream on the way to the event structure (which counts as deep voodoo), define 'event_callback' and have it modify its @_.
'exclusive_event_callback' => CODEREF: Just like 'event_callback'; but if you specify this, the callback is called instead of adding the events to the event structure. (So the event structure returned by decode() at the end will always be empty.) Good for cases like the text dumper in the Synopsis, above.

MIDI::Event::encode( \@events, {...options...}): This takes a reference to an event structure (a LoL) and encodes it as binary data, which it returns a reference to. Options:

'unknown_callback' => CODEREF: If this is specified, it's interpreted as a reference to a subroutine to be called when an unknown event name (say, 'macro_10' or something), is seen by encode(). The function is fed all of the event (its name, delta-time, and whatever parameters); the return value of this function is added to the encoded data stream -- so if you don't want to add anything, be sure to return ''.
If no 'unknown_callback' is specified, encode() will "warn" (well, "carp") of the unknown event. To merely block that, just set 'unknown_callback' to "sub{return('')}"
'no_eot_magic' => 0 or 1: Determines whether a track-final 0-length text event is encoded as a end-track event -- since a track-final 0-length text event probably started life as an end-track event read in by decode(), above.
'never_add_eot' => 0 or 1: If 1, "encode()" never ever adds an end-track (EOT) event to the encoded data generated unless it's explicitly there as an 'end_track' in the given event structure. You probably don't ever need this unless you're encoding for straight writing to a MIDI port, instead of to a file.
'no_running_status' => 0 or 1: If 1, disables MIDI's "running status" compression. Probably never necessary unless you need to feed your MIDI data to a strange old sequencer that doesn't understand running status.

Note: If you're encoding just a single event at a time or less than a whole trackful in any case, then you probably want something like:

          $data_r = MIDI::Event::encode(
            [
              [ 'note_on', 141, 4, 50, 64 ]
            ],
            { 'never_add_eot' => 1} );

which just encodes that one event as an event structure of one event -- i.e., an LoL that's just a list of one list.

But note that running status will not always apply when you're encoding less than a whole trackful at a time, since running status works only within a LoL encoded all at once. This'll result in non-optimally compressed, but still effective, encoding.

MIDI::Event::copy_structure()

This takes a reference to an event structure, and returns a reference to a copy of it. If you're thinking about using this, you probably should want to use the more straightforward

          $track2 = $track->copy

instead. But it's here if you happen to need it.

EVENTS AND THEIR DATA TYPES

DATA TYPES

Events use these data types:

channel = a value 0 to 15
note = a value 0 to 127
dtime = a value 0 to 268,435,455 (0x0FFFFFFF)
velocity = a value 0 to 127
channel = a value 0 to 15
patch = a value 0 to 127
sequence = a value 0 to 65,535 (0xFFFF)
text = a string of 0 or more bytes of of ASCII text
raw = a string of 0 or more bytes of binary data
pitch_wheel = a value -8192 to 8191 (0x1FFF)
song_pos = a value 0 to 16,383 (0x3FFF)
song_number = a value 0 to 127
tempo = microseconds, a value 0 to 16,777,215 (0x00FFFFFF)

For data types not defined above, (e.g., sf and mi for 'key_signature'), consult MIDI::Filespec and/or the source for "MIDI::Event.pm". And if you don't see it documented, it's probably because I don't understand it, so you'll have to consult a real MIDI reference.

EVENTS

And these are the events:

('note_off', dtime, channel, note, velocity)
('note_on', dtime, channel, note, velocity)
('key_after_touch', dtime, channel, note, velocity)
('control_change', dtime, channel, controller(0-127), value(0-127))
('patch_change', dtime, channel, patch)
('channel_after_touch', dtime, channel, velocity)
('pitch_wheel_change', dtime, channel, pitch_wheel)
('set_sequence_number', dtime, sequence)
('text_event', dtime, text)
('copyright_text_event', dtime, text)
('track_name', dtime, text)
('instrument_name', dtime, text)
('lyric', dtime, text)
('marker', dtime, text)
('cue_point', dtime, text)
('text_event_08', dtime, text)
('text_event_09', dtime, text)
('text_event_0a', dtime, text)
('text_event_0b', dtime, text)
('text_event_0c', dtime, text)
('text_event_0d', dtime, text)
('text_event_0e', dtime, text)
('text_event_0f', dtime, text)
('end_track', dtime)
('set_tempo', dtime, tempo)
('smpte_offset', dtime, hr, mn, se, fr, ff)
('time_signature', dtime, nn, dd, cc, bb)
('key_signature', dtime, sf, mi)
('sequencer_specific', dtime, raw)
('raw_meta_event', dtime, command(0-255), raw)
('sysex_f0', dtime, raw)
('sysex_f7', dtime, raw)
('song_position', dtime)
('song_select', dtime, song_number)
('tune_request', dtime)
('raw_data', dtime, raw)

Three of the above events are represented a bit oddly from the point of view of the file spec:

The parameter pitch_wheel for 'pitch_wheel_change' is a value -8192 to 8191, although the actual encoding of this is as a value 0 to 16,383, as per the spec.

Sysex events are represented as either 'sysex_f0' or 'sysex_f7', depending on the status byte they are encoded with.

'end_track' is a bit stranger, in that it is almost never actually found, or needed. When the MIDI decoder sees an EOT (i.e., an end-track status: FF 2F 00) with a delta time of 0, it is ignored! If in the unlikely event that it has a nonzero delta-time, it's decoded as a 'text_event' with whatever that delta-time is, and a zero-length text parameter. (This happens before the 'event_callback' or 'exclusive_event_callback' callbacks are given a crack at it.) On the encoding side, an EOT is added to the end of the track as a normal part of the encapsulation of track data.

I chose to add this special behavior so that you could add events to the end of a track without having to work around any track-final 'end_track' event.

However, if you set "no_eot_magic" as a decoding parameter, none of this magic happens on the decoding side -- 'end_track' is decoded just as it is.

And if you set "no_eot_magic" as an encoding parameter, then a track-final 0-length 'text_event' with non-0 delta-times is left as is. Normally, such an event would be converted from a 'text_event' to an 'end_track' event with thath delta-time.

Normally, no user needs to use the "no_eot_magic" option either in encoding or decoding. But it is provided in case you need your event LoL to be an absolutely literal representation of the binary data, and/or vice versa.

MIDI BNF

For your reference (if you can make any sense of it), here is a copy of the MIDI BNF, as I found it in a text file that's been floating around the Net since the late 1980s.

Note that this seems to describe MIDI events as they can occur in MIDI-on-the-wire. I think that realtime data insertion (i.e., the ability to have <realtime byte>s popping up in the middle of messages) is something that can't happen in MIDI files.

In fact, this library, as written, can't correctly parse MIDI data that has such realtime bytes inserted in messages. Nor does it support representing such insertion in a MIDI event structure that's encodable for writing to a file. (Although you could theoretically represent events with embedded <realtime byte>s as just "raw_data" events; but then, you can always stow anything at all in a "raw_data" event.)

 1.  <MIDI Stream> ::=           <MIDI msg> < MIDI Stream>
 2.  <MIDI msg> ::=              <sys msg> | <chan msg>
 3.  <chan msg> ::=              <chan 1byte msg> |
                                 | <chan 2byte msg>
 4.  <chan 1byte msg> ::=        <chan stat1 byte> <data singlet>
                                   <running singlets>
 5.  <chan 2byte msg> ::=        <chan stat2 byte> <data pair>
                                   <running pairs>
 6.  <chan stat1 byte> ::=       <chan voice stat1 nibble>
                                   <hex nibble>
 7.  <chan stat2 byte> ::=       <chan voice stat2 nibble>
                                   <hex nibble>
 8.  <chan voice stat1 nyble>::= C | D
 9.  <chan voice stat2 nyble>::= 8 | 9 | A | B | E
 10. <hex nyble> ::=             0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
                                 | 8 | 9 | A | B | C | D | E | F
 11. <data pair> ::=             <data singlet> <data singlet>
 12. <data singlet> ::=          <realtime byte> <data singlet> |
                                 | <data byte>
 13. <running pairs> ::=         <empty> | <data pair> <running pairs>
 14. <running singlets> ::=      <empty> |
                                 | <data singlet> <running singlets>
 15. <data byte> ::=             <data MSD> <hex nyble>
 16. <data MSD> ::=              0 | 1 | 2 | 3 | 4 | 5 | 6 | 7
 17. <realtime byte> ::=         F8 | FA | FB | FC | FE | FF
 18. <sys msg> ::=               <sys common msg> |
                                 | <sysex msg> |
                                 | <sys realtime msg>
 19. <sys realtime msg> ::=      <realtime byte>
 20. <sysex msg> ::=             <sysex data byte>
                                   <data singlet> <running singlets>
                                   <eox byte>
 21. <sysex stat byte> ::=       F0
 22. <eox byte> ::=              F7
 23. <sys common msg> ::=        <song position msg> |
                                 | <song select msg> |
                                 | <tune request>
 24. <tune request> ::=          F6
 25. <song position msg> ::=     <song position stat byte>
                                   <data pair>
 26. <song select msg> ::=       <song select stat byte>
                                   <data singlet>
 27. <song position stat byte>::=F2
 28. <song select stat byte> ::= F3

COPYRIGHT

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

Sean M. Burke "sburke@cpan.org" (Except the BNF -- who knows who's behind that.)

2022-10-13

perl v5.34.0