phpMan > man > MIDI::Track(3pm)

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.)

    track->skyline({ ...options... })
        skylines the entire track. Modifies the track. See MIDI::Score for documentation on skyline

    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
        Perl code that 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 to 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 AT cpan.org" (until 2010)

    Darrell Conklin "conklin AT cpan.org" (from 2010)