C++ MIDI Library - FAQ

A:

First, take a look at tests/jdkmidi_rewrite_midifile.cpp

It reads a midifile and then writes it out. You want to write out a file of your own events.

First you must create and fill in a MultiTrack object with your data:

   // the object which will hold all the tracks
    jdkmidi::MIDIMultiTrack tracks;

    tracks.SetClksPerBeat( 24 );

Create individual midi events with the MIDITimedBigMessage and add them to a track:

    {
        MIDITimedBigMessage m;
        m.SetTime( 24 );
        m.SetNoteOn( channel, note, velocity );

        if( !tracks.GetTrack(1)->PutEvent( m ) ) { abort(); }

        m.SetTime( 48 );
        m.SetNoteOff( channel, note, 0 );

        if( !tracks.GetTrack(1)->PutEvent( m ) ) { abort(); } // add messages in time order!
    }

Track 0 is used for tempo and time signature info:

    {
        MIDITimedBigMessage m;
        m.SetTime( 0 );
        m.SetTimeSig( 4, 4 );  

        if( !tracks.GetTrack(0)->PutEvent( m ) ) { abort(); }

        m.SetTime( 0 );
        m.SetTempo32( 120 * 32 ); // tempo stored as bpm * 32, giving 1/32 bpm resolution

        if( !tracks.GetTrack(0)->PutEvent( m ) ) { abort(); }
    }

To write the multi track object out, you need to create an output stream for the output filename:

   // create the output stream
    jdkmidi::MIDIFileWriteStreamFileName out_stream( outfile_name );

And then output the stream like my example does, except setting num_tracks and division to match your data.

    int num_tracks = 2;
    int division = 24;

    if( out_stream.IsValid() )
    {
      // the object which takes the midi tracks and writes the midifile to the output stream
      jdkmidi::MIDIFileWriteMultiTrack writer(
        &tracks,
        &out_stream
        );

      // write the output file
      if( writer.Write( num_tracks, division ) )
      {
        return_code = 0;
      }
      else
      {
        fprintf( stderr, "Error writing file '%s'\n", outfile_name );
      }
     }

Also see the specification at: http://www.sonicspot.com/guide/midifiles.html