Andy Pike - DirectX 8 Programming Tutorial

Midi files

Midi stands for "Musical Instrument Digital Interface". Midi files do not actually contain music recordings, instead they hold a set of instructions on how to play a tune. Midi files are very small which is good if you plan to have a downloadable version of your game on a website. The quality of playback dependents on the sound card of your user's machine. A Midi sequence that sounds great on a high-end card may sound terrible on a cheap one. Also, Midi is for instrumentals only, not vocals.

Mp3 files

As with wav files, mp3 files are actual digital recordings. But the major difference between mp3 and wav is that mp3 files are compressed, and are typically one-tenth the size of uncompressed files. Because mp3 files are compressed, they are a lossy format. This means that depending on how they are compressed, a certain degree of quality will be lost. However, you can still get "almost" CD quality audio from an mp3 file as long as the compression settings are right. Also, mp3 files are a "streaming media" that means that when they are played the whole track is not loaded at the start. Instead, only a part of the track is loaded from disk at a time as it is required.

My preference

I would say that you probably want to use mp3 or midi files for background music. Especially if you want your users to download you game from a website. Mp3 and midi files are both small and therefore good for long background tracks. I would then tend to use wav files for short sound effects like explosions and power-ups for that extra bit of quality. If file size is not a problem, then why not use wav files for all sounds and music?

Before we can start the actual coding, we need to add some new header and library files to our project. I've included the new header files in Game.h just below where I have included d3dx8.h. You can add the library files by going to Project > Settings… then on the Link tab, type the new library file names into the Object/Library Modules input box. The new files are listed below:

· dmusici.h

· dsound.h

· dshow.h

· dsound.lib

· strmiids.lib

To setup DirectX Audio we need to create two objects: the performance object and the loader object. The performance object is the top-level object in DirectX Audio, it handles the flow of data from the source to the synthesizer. The loader object loads the files (wav and midi) into sound segments that can be played later. We only need one of each of these objects for the whole application, so we will create them as member variables of our CGame class. Their definitions are shown below:

IDirectMusicPerformance8* m_pDirectAudioPerformance;

IDirectMusicLoader8* m_pDirectAudioLoader;

Before we can create our objects, we need to initialise the COM library. We need to do this because DirectX Audio is pure COM. Don't worry too much about what this means, all you need to do is call the CoInitialize function (shown below) before you can create the DirectX Audio objects. To keep it simple, this is done in the CGame constructor.

CoInitialize(NULL);

Now that we have initialised COM, we need to create and initialise our two DirectX Audio objects. To do this, we have a new method of CGame called InitialiseDirectAudio which is shown below. This method is called from our Initialise method, take a look at the code and I'll explain in a moment.

bool CGame::InitialiseDirectAudio(HWND hWnd) {

LogInfo("
Initialise DirectAudio:");

//Create the DirectAudio performance object

if (CoCreateInstance(CLSID_DirectMusicPerformance, NULL, CLSCTX_INPROC, IID_IDirectMusicPerformance8, (void**) &m_pDirectAudioPerformance) != S_OK) {

LogError("