NAME¶
MIDI::Track -- functions and methods for MIDI tracks
SYNOPSIS¶
use MIDI; # ...which "use"s MIDI::Track et al
$taco_track = MIDI::Track->new;
$taco_track->events(
['text_event', 0, "I like tacos!"],
['note_on', 0, 4, 50, 96 ],
['note_off', 300, 4, 50, 96 ],
);
$opus = MIDI::Opus->new(
{ 'format' => 0, 'ticks' => 240, 'tracks' => [ $taco_track ] }
);
...etc...
DESCRIPTION¶
MIDI::Track provides a constructor and methods for objects representing a MIDI
track. It is part of the MIDI suite.
MIDI tracks have, currently, three attributes: a type, events, and data. Almost
all tracks you'll ever deal with are of type "MTrk", and so this is
the type by default. Events are what make up an MTrk track. If a track is not
of type MTrk, or is an unparsed MTrk, then it has (or better have!) data.
When an MTrk track is encoded, if there is data defined for it, that's what's
encoded (and "encoding data" means just passing it thru untouched).
Note that this happens even if the data defined is "" (but it won't
happen if the data is undef). However, if there's no data defined for the MTrk
track (as is the general case), then the track's events are encoded, via a
call to "MIDI::Event::encode".
(If neither events not data are defined, it acts as a zero-length track.)
If a non-MTrk track is encoded, its data is encoded. If there's no data for it,
it acts as a zero-length track.
In other words, 1) events are meaningful only in an MTrk track, 2) you probably
don't want both data and events defined, and 3) 99.999% of the time, just
worry about events in MTrk tracks, because that's all you ever want to deal
with anyway.
CONSTRUCTOR AND METHODS¶
MIDI::Track provides...
- the constructor MIDI::Track->new({ ...options... })
- This returns a new track object. By default, the track is
of type MTrk, which is probably what you want. The options, which are
optional, is an anonymous hash. There are four recognized options:
"data", which sets the data of the new track to the string
provided; "type", which sets the type of the new track to the
string provided; "events", which sets the events of the new
track to the contents of the list-reference provided (i.e., a reference to
a LoL -- see perllol for the skinny on LoLs); and "events_r",
which is an exact synonym of "events".
- the method $new_track = $track->copy
- This duplicates the contents of the given track, and
returns the duplicate. If you are unclear on why you may need this
function, consider:
$funk = MIDI::Opus->new({'from_file' => 'funk1.mid'});
$samba = MIDI::Opus->new({'from_file' => 'samba1.mid'});
$bass_track = ( $funk->tracks )[-1]; # last track
push(@{ $samba->tracks_r }, $bass_track );
# make it the last track
&funk_it_up( ( $funk->tracks )[-1] );
# modifies the last track of $funk
&turn_it_out( ( $samba->tracks )[-1] );
# modifies the last track of $samba
$funk->write_to_file('funk2.mid');
$samba->write_to_file('samba2.mid');
exit;
So you have your routines funk_it_up and turn_it_out, and they each modify
the track they're applied to in some way. But the problem is that the
above code probably does not do what you want -- because the last
track-object of $funk and the last track-object of $samba are the same
object. An object, you may be surprised to learn, can be in different
opuses at the same time -- which is fine, except in cases like the above
code. That's where you need to do copy the object. Change the above code
to read:
push(@{ $samba->tracks_r }, $bass_track->copy );
and what you want to happen, will.
Incidentally, this potential need to copy also occurs with opuses (and in
fact any reference-based data structure, altho opuses and tracks should
cover almost all cases with MIDI stuff), which is why there's
$opus->copy, for copying entire opuses.
(If you happen to need to copy a single event, it's just $new = [@$old] ;
and if you happen to need to copy an event structure (LoL) outside of a
track for some reason, use MIDI::Event::copy_structure.)
- the method $track->events( @events )
- Returns the list of events in the track, possibly after
having set it to @events, if specified and not empty. (If you happen to
want to set the list of events to an empty list, for whatever reason, you
have to use "$track->events_r([])".)
In other words: $track->events(@events) is how to set the list of events
(assuming @events is not empty), and @events = $track->events is how to
read the list of events.
- the method $track->events_r( $event_r )
- Returns a reference to the list of events in the track,
possibly after having set it to $events_r, if specified. Actually,
"$events_r" can be any listref to a LoL, whether it comes from a
scalar as in $some_events_r, or from something like "[@events]",
or just plain old "\@events"
Originally $track->events was the only way to deal with events, but I
added $track->events_r to make possible 1) setting the list of events
to (), for whatever that's worth, and 2) so you can directly manipulate
the track's events, without having to copy the list of events
(which might be tens of thousands of elements long) back and forth. This
way, you can say:
$events_r = $track->events_r();
@some_stuff = splice(@$events_r, 4, 6);
But if you don't know how to deal with listrefs outside of LoLs, that's OK,
just use $track->events.
- the method $track->type( 'MFoo' )
- Returns the type of $track, after having set it to 'MFoo',
if provided. You probably won't ever need to use this method, other than
in a context like:
if( $track->type eq 'MTrk' ) { # The usual case
give_up_the_funk($track);
} # Else just keep on walkin'!
Track types must be 4 bytes long; see MIDI::Filespec for details.
- the method $track->data( $kooky_binary_data )
- Returns the data from $track, after having set it to
$kooky_binary_data, if provided -- even if it's zero-length! You probably
won't ever need to use this method. For your information,
$track->data(undef) is how to undefine the data for a track.
- the method $track->new_event('event', ...parameters...
)
- This adds the event ('event', ...parameters...) to the end
of the event list for $track. It's just sugar for:
push( @{$this_track->events_r}, [ 'event', ...params... ] )
If you want anything other than the equivalent of that, like some kinda
splice(), then do it yourself with $track->events_r or
$track->events.
- the method $track->dump({ ...options... })
- This dumps the track's contents for your inspection. The
dump format is code that looks like Perlcode you'd use to recreate that
track. This routine outputs with just "print", so you can use
"select" to change where that'll go. I intended this to be just
an internal routine for use only by the method MIDI::Opus::dump, but I
figure it might be useful to you, if you need te dump the code for just a
given track. Read the source if you really need to know how this
works.
COPYRIGHT¶
Copyright (c) 1998-2002 Sean M. Burke. All rights reserved.
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"