Title:       Playing Midi files with DirectMusic  	
Author:      Carlos Jiménez de Parga 
Email:       cjimenez@servitel.es
Environment: VC++ 6.0, NT 4.0,2000 Server, Win95/98
Keywords:    DirectX Audio Class
Level:       
Description: A DirectX 8 class to perform Midi music playback.
Section      Audio & Video
SubSection   DirectMusic 

• Download executable demo project (DirectX 8 required) - 151Kb

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), segment files (.sgt) and PCM waveform files
(.wav). 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 directosund buffer, instead, it goes to an audiopath which controls data flow from a performance to the final output. The adudiopath
  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 synthetizer.
• FX (Reverb, Chorus...) if it is available in the software synthetizer.
• 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 diferents sets of musical variations
  and changes in the chords progress. 
• 3D Positioning.

Main Intefaces of DirectMusic

IDirectMusic8: This interface allows managing buffers and ports. There should only exist one instance of this
interface per aplication.

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
sinthesizer.

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 diferent 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 aplication, 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 is necesary 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 necesary to include in the project the header "dmusic.h" and "dmusic.cpp" file and finally declare a dinamic variable of CMidiMusic class 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 class 
	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++;  // It is necessary
	}

	 // Read the file and specify if it is a mid file or not 
	pMidi->LoadMidiFromFile("c:/music/song_004.mid",TRUE);
	 // Play the file
	pMidi->Play();
	AfxMessageBox("Playing...");
	 // Stop it
	pMidi->Stop();
	 //Important!: Delete the dinamic variable in order to call the destructor 
	 //which call the DirectMusic releases interfaces
	
	delete pMidi;
}

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.

Overview of the demo project

As you can see, this is not WinAmp, wish it was ;) Nevertheless, all of CMidiMusic class features are made available.