Playing Midi Files with DirectMusic

Introduction

This article focuses on the use of CMidiMusic which allows an easy access to DirectX DirectMusic API. This class allows loading and playing general midi sequence files(.mid). The class is designed to perform midi playback in one segment and offers additional features like using any midi port installed in your system, 3D sound environment, sound effects, etc.

Direct Audio Specifications

The DirectX 8.0 Audio part offers improved integration between DirectSound and DirectMusic, including a great set of new features. Some of these are listed hereafter:

The last version of Direct Audio allows using hardware acceleration for sound synthesis.
With the new AudioPath model, the sound of a port does not go directly to a directsound buffer, instead, it goes to an audiopath which controls data flow from a performance to the final output. The audiopath allows controlling the 3D position of each sound and adding other effects.
The segments are modified independently and you can apply effects like pan, volume, individually.
It allows using DLS2 (Downloadable sound level 2 standard) which provides a great sound quality and unlimited use of instruments with the software synthesizer.
FX (Reverb, Chorus...) if it is available in the software synthesizer.
It overcomes the 16 midi channels limit, allowing the use of as many midi channels as the software is able to handle.
The playback can be controlled accurately in run time by selecting different sets of musical variations and changes in the chords progress.
3D Positioning.

Main Interfaces of DirectMusic

IDirectMusic8: This interface allows managing buffers and ports. There should only exist one instance of this interface per application.
IDirectMusicPerformance8: This is the most important interface in playback management. It is used to add and remove ports, play segments, notify event reception, control music parameters and obtain timing information.
IDirectMusicPort8: This interface provides access to DirectMusicPorts objects like MPU-401 or the software synthesizer.
IDirectMusicSegment8: This interface represents a segment, musical piece made up of multiple tracks. It can contain a midi file, a wave, a segment.
IDirectMusicLoader8: Its main function is to find and load the different objects. These objects are to be stored in a segment.
IDirectMusicSegmentState8: The (playback) engine creates a SegmentState object which allows analyzing the state of the segment currently playing.
IDirectMusicAudioPath8: The IDirectMusicAudioPath8 interface represents the stages of data flow from the data file to the primary buffer.

DirectMusic Architecture

Once a resource has been loaded in a segment, the performance dispatches the messages defined by a tool of an application, such tools are grouped in toolgraphs which process specific segment messages. A tool can modify a message and pass it on, delete it, or send a new message.

Finally, the messages are delivered to the output tool, which converts the data to MIDI format before passing it to the synthesizer. Channel-specific MIDI messages are directed to the appropriate channel group on the synthesizer. The synthesizer creates sound waves and streams them to a device called a sink, which manages the distribution of data through buses to DirectSound buffers.

There are three kinds of buffers:

Sink-in buffers are DirectSound secondary buffers into which the sink streams data. Here are applied many effects like 3D, pan, volume, etc...The resulting waveform is passed either directly to the primary buffer or to one or more mix-in buffers.
Mix-in buffers receive data from other buffers, apply effects, and mix the resulting wave forms. These buffers can be used to apply global effects.
The primary buffer performs the final mixing on all data and passes it to the rendering device.

The following diagram shows the flow of data from files to the speakers:

Using CMidiMusic

In first sight, it is necessary to add in Visual C++ IDE this library: Go to Project -> Settings -> Object Library Modules and add dxguid.lib of DirectX8 SDK.

After this, it will be necessary to include in the project the header "dmusic.h" and "dmusic.cpp" file and finally instance an object of CMidiMusic class type as shown below:

void CPlayerDlg::OnButton_Start()     
{
    DWORD dwcount; // Counter variable to enumerate the midi ports 
    INFOPORT Info; // INFOPORT structure to store port information 
    BOOL bSelected;

    CMidiMusic *pMidi;     // Pointer to CMidiMusic object type
    pMidi=new CMidiMusic;     // Allocate it      
    pMidi->Initialize(FALSE);// Initialize without 3D positioning
    
    dwcount=0;
    bSelected=FALSE;
    
     // Port enumeration  phase 
     // It is necessary to supply a port counter 
    while (pMidi->PortEnumeration(dwcount,&Info)==S_OK)
    {
        // Ensure it is an output hardware device
        if (Info.dwClass==DMUS_PC_OUTPUTCLASS) 
        {
            if (!((Info.dwFlags & DMUS_PC_SOFTWARESYNTH) || bSelected))
            {
                // Select the enumerated port 
                pMidi->SelectPort(&Info);
                bSelected=TRUE;
            }
        }
    
    dwcount++;      
   }

     // Read the MIDI file 
    pMidi->LoadMidiFromFile("c:\\music\\song_004.mid");
     // Play the file
    pMidi->Play();
    AfxMessageBox("Playing...");
     // Stop it
    pMidi->Stop();

    //Important!: Delete the pointer to the object in order to call the 
    //destructor 
    //which call the DirectMusic releases interfaces
    delete pMidi;
}

CMidiMusic Capabilities

Synthesizer	3D	Effects (Reverb,Chorus)
Microsoft Software	Yes	Only in not 3D mode
Hardware	No	No
External	No	No

More Information

For more information about the CMidiMusic class, read the attached file readme.txt included in the sources. You will be able to find more information in the online help of http://www.microsoft.com/directx and DirectX 8 SDK technical documentation.