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Sound Formats and Their Uses in Games
After seeing that people wanted a bit more substance to my article, I decided that I would add some meat to it. I apologize for the huge delay in rewriting this thing like I said I would, but things came up, blah blah blah. The point is that I finished it and this go around we'll have some tutorials using different APIs to play various formats. Hope you enjoy it, or at least learn a little something from it. First, let's talk about what to look for in a file when making a game. What are our needs? Probably at the top of the list for most people is quality. We want our audience to enjoy every aspect of the experience that we are trying to provide them when they are playing our game. If the graphics for your game are bad not many people are going to want to play it; the same can be said for low quality sound. As an example of the importance of sound, turn the volume off when playing your favorite game and see if it's as much fun. Sound adds to the immersion that people want when playing a game. If you don't have good quality sound, it will detract from this immersion. The next thing to look for when selecting a file type is the resulting file size. Today, people don't want to wait for the game to load, they want instant gratification. From a development standpoint we can't always give them that; all media, of course, has to be loaded in order to be used. Now granted, with increasing computing power and larger amounts of RAM (measuring in the gigabytes in some cases) loading times are decreasing significantly. Bear in mind however that everyone is not a diehard gamer or developer and is not likely to beef up their systems to play such resource intensive games. The demographic that you may be shooting for might be casual or older gamers that just want to play something quick, possibly something to pass time on a break at work. When choosing the format to use in your project you should take all of this into consideration as well as the documentation of the desired filetype. Formats.WAV As a running example of compression technologies, I have used Sonic Foundry Sound Forge 5.0 and extracted a song from a CD. I first saved it as a .WAV with the following parameters: Sample rate: 44,100 Hz
This song came out to be 47.9 MB as a raw WAV file with no compression. We'll see what we can get this down to in the end :). As a note, WAV files can have compression in them using various codecs. All APIs do not automatically support compressed WAVs, however. To show WAV compression I used Sound Forge and saved the file as the IMA ADPCM format which had the following parameters: 44,100 kHz, 4 bit, stereo. This version output a file of 12 MB. So, we have a WAV with compression. The file size is greatly reduced, but not enough for me. I may not have used the best compressor for the WAV file, but this just shows that WAV compression is definitely possible, though not as good as other formats. Bottom Line- Well Documented and easy to use. File size can get pretty large unless you choose to use codecs for them. Good choice to use for sound effects or other small audio pieces. .MP3 The resultant file was 4.34 MB. Not bad, we're getting somewhere. As a test, I changed the WAV file again to MP3, but this time using the 64 Kbps FM Radio Quality Audio selection from the template button. The output file was 2.17 MB, but the quality wasn't nearly as good, as was to be expected. When doing audio for games you want to balance between size and quality, this was apparently too big of a leap. Bottom Line- Well documented, many examples online. Good format to use for a lot of speech or music. .OGG To show the compression technology of the OGG format, I downloaded a program found on the www.vorbis.com site. http://www.vorbis.com/files/1.0/windows/oggdrop-win32.zip This utility takes audio files and lets you drop them into the window and converts them to the .OGG file for you. You can change parameters for the application, and I played around with the quality settings to get a good balance between quality and size. I first set the quality setting in the utility to 1.0 as someone had suggested to me. The quality was ok, but I could tell that it wasn't anywhere close to the original. I played around with it until I got a suitable sound at quality setting 2. The .OGG I got was 2.99 MB and sounded good! Very cool. As a note about the previous version of this article, I was using Sound Forge to convert to the OGG format and at that time the best compression for the OGG file was a bit higher than an MP3, but using the utility from the site, presumably much newer, I got this decrease in size. Bottom Line- Best compression found in this experiment for song quality audio. Some neat utilities can be found on the site to help you convert your songs to the format without having to write code to do it yourself (always a plus). MIDI Now, when you think about games these days you don't immediately think of MIDI files as being used, right? Wrong. Although the end format may not be a .MID(I), composers in film and games use the MIDI format quite extensively to quickly setup their musical pieces. The thing to remember about MIDIs is that the bleeps and boops you think of when thinking about MIDIs are not the only sounds available. I'm not a composer myself, just a lowly programmer, but in my research for this article I have found that you can get different Instrument Definition Files (IDF) to use in the MIDIs. These files are what make or break the sound coming from your speakers when you play a MIDI. You can have the less than pleasing bleeps, or, you can have a song that would rival an MP3 in its sound. It all depends on your IDF. Here's a recent thread in the Music and Sound Forum where people who actually do compose music can explain the technicalities of music composition for games as it relates to the MIDI format much better than I can. Lucky for us though, our job is not to make music, our job as programmers is to make the music play. Bottom Line- MIDIs can be fairly small in size and if given the right IDF can sound great. The format has been around for a long time and because of that there many examples and samples available all over the net. For more information on the above formats and others check http://www.wotsit.org, they have a lot of good information on just about any format you can imagine. APIsI will go over a couple of APIs that will allow you to play sound files for your games. I'll show an example of playing .OGG, MIDI, MP3 and .WAV files. The examples I will show you will be in APIs that are compatible across many different platforms, so no matter what OS you're running you should have little to no trouble in getting the examples working for your particular setup. Now, on to the code... SDLI was turned on to SDL when I was browsing the bookshelves at Borders and came across Ernest Pazera's book, Focus on SDL. I highly recommend it. SDL, for those of you who may not know, is a library put together to be as cross-platform compatible as possible. This is very nice to have, as building a version for a different system (Linux for example), requires in most cases nothing more than building it with the correct set of libraries for that OS. This is assuming, however, that you are writing little to no OS specific code. Standard C/C++ should compile fine. As of this writing, the newest SDL_mixer version is 1.2.5. This version is very flexible and easier (if that's possible with SDL) to use. The developers of the library have made it support loading of OGG files without having to build your program with the libraries for the OGG format. You'll love the simplicity of SDL if you're not already familiar with it. Now, before we get on to the code, you're going to need to setup your development environment. Instead of reinventing the wheel here, I'll refer you to an article written by Mr. Pazera on this very topic. Once you've setup the compiler you're ready to do some coding with SDL_mixer. The following program sets up a very basic window for SDL and initializes the SDL_mixer. Next, the program loads in the specified music file (in the case of the below program, the file to be played is in the project folder). Next you play it and loop, and finally you do some cleanup functions. Easy. WAV
#include "sdl.h"
#include "sdl_mixer.h"
#include <stdlib.h>
SDL_Surface* surface = NULL; //sets up your video surface
SDL_Event event; //event structure
Mix_Music* music; //music object
//main function
int main(int argc, char* argv[])
{
//initialize SDL
if (SDL_Init(SDL_INIT_VIDEO)==-1)
{
//error initializing SDL
//report the error
fprintf(stderr,"Could not initialize SDL!\n");
//end the program
exit(1);
}
else
{
//SDL initialized
//report success
fprintf(stdout,"SDL initialized properly!\n");
//set up to uninitialize SDL at exit
atexit(SDL_Quit);
}
//create windowed environment
/*First parameter is screen width, second is for screen height, third param is for bit
depth, and the last parameter is for different flags to be set, in this case: SDL_ANYFORMAT
serves to use the pixel format of the actual display surface*/
surface = SDL_SetVideoMode(640, 480,0,SDL_ANYFORMAT);
//error check
if (surface == NULL)
{
//report error
fprintf(stderr,"Could not set up display surface!\n");
//exit the program if we have an error
exit(1);
}
//start up sdl_mixer
Mix_OpenAudio(MIX_DEFAULT_FREQUENCY,MIX_DEFAULT_FORMAT,1,4096);
Mix_Chunk *sample; //load in the music
sample=Mix_LoadWAV("filename.wav");
if(Mix_PlayChannel(-1, sample, 1)==-1) {
//error
}
//repeat
for(;;)
{
//wait for an event
if(SDL_PollEvent(&event)==0)
{
//update screen
SDL_UpdateRect(surface,0,0,0,0);
}
else
{
//event occurred, check for quit
if(event.type==SDL_QUIT) break;
}
}
//clean up
Mix_FreeChunk(sample);
sample=NULL;//make sure we free it
Mix_CloseAudio();
return(0);
}
Now on to one of the newer formats: OGG. Well, you may be thinking that this is going to take some fiddling and working to get up and running properly. No need to worry though. With this new version of the library, the OGG format is automatically supported, so the only thing that you have to do is change one setting of the above code to get it to play an OGG: sample=Mix_LoadWAV("filename.ogg"); Pretty cool, huh? FYI: As a test of the flexibility of the SDL_mixer library, I tried to play the compressed WAV that I made earlier as well as the regular WAV file. SDL required nothing special to be done, just simply telling it what file to play is all that is needed. There's no headache in using compressed WAVs as far as SDL is concerned. This has the benefit of you not having to fuss with some tricky code to get working and leave you to focus on your game, which is the important thing anyway. SDL_mixer doesn't have native MP3 support as of this release, you need to have another library (SMPEG) installed for it to work. MIDI MIDI files, as I said earlier, are not usually used today as is in games. If, however, you need to play a MIDI in a game, here's how. Playing MIDIs is a bit different than playing WAVs or OGGs. Instead of this block of code to play OGGs and such:
Mix_Chunk *sample; //load in the music
sample=Mix_LoadWAV("filename.wav");
if(Mix_PlayChannel(-1, sample, 1)==-1) {
//error
}
We use this, which uses Music instead of chunk functions:
Mix_Music *music; //load in the music
music=Mix_LoadMUS("filename.midi");
if(Mix_PlayMusic(music, -1)==-1){
//error
}
And that's all you have to do to change over and play this new set of audio files (which include WAVE, MOD, MIDI, OGG, MP3 (if you have SMPEG installed)). Since we used a different initialization function and playing function for our file, we in turn need to use a different cleanup function. Instead of: Mix_FreeChunk(sample); sample=NULL; //make sure we free it We use: Mix_FreeMusic(music); music=NULL; //make sure we free it Ok, we've covered how to play 3 (well, 4 if you count the compressed WAV file, which took nothing extra to accomplish) different file types using the SDL_mixer library, but these are not the only formats that can be played with the above code according to the library docs found at http://jcatki.no-ip.org/SDL_mixer/SDL_mixer_frame.html (a very good resource). The above code will play WAVE, AIFF, RIFF, and VOC files. This flexibility is a huge benefit to us as programmers, no need in writing multiple loaders and players when it has already been done for you. FMODAs of this writing this is my first encounter with FMOD, but I'll be the first to say that it's pretty easy to get up and running with it. FMOD is a great little sound system that you can plop into about any machine from Windows to Linux, and XBox to Gamecube, they've got all the bases covered. FMOD is, as I said, extremely easy to get up and running, dare I say, easier than SDL_mixer. As hard as that may be to believe, I think it's true. SDL required a lot of little initialization functions, not so with FMOD. Here's a crash course on setting up FMOD in VC++. Download the API from here: www.fmod.org Unzip to an easy to find place (mine's on the desktop). Now, fire up MVC++ go to Tools->Options and click the directories tab. Make a new entry for Include files and go to the folder you unzipped to and go to API->Inc. Now switch to Library files in the drop down box and do the same as above but click through to lib. Finally click OK. Now, for the project settings, click Project->Settings and click the link tab. Under Object/Library Modules type fmodvc.lib at the beginning, and you're all set. One last thing, since we're using SDL to setup a window, go ahead and setup those project settings too. Lastly, make sure that you put SDL.dll and fmod.dll in your project folder. OK, now we're ready to do some coding.
#include "sdl.h"
#include "fmod.h"
#include <stdlib.h>
SDL_Surface* surface = NULL; //sets up your video surface
SDL_Event event; //event structure
//main function
int main(int argc, char* argv[])
{
//initialize SDL
if (SDL_Init(SDL_INIT_VIDEO)==-1)
{
//error initializing SDL
//report the error
fprintf(stderr,"Could not initialize SDL!\n");
//end the program
exit(1);
}
else
{
//SDL initialized
//report success
fprintf(stdout,"SDL initialized properly!\n");
//set up to uninitialize SDL at exit
atexit(SDL_Quit);
}
//create windowed environment
/*First parameter is screen width, second is for screen height, third param is for bit
depththe last parameter is for different flags to be set, in this case: SDL_ANYFORMAT
serves to use the pixel format of the actual display surface*/
surface = SDL_SetVideoMode(640, 480,0,SDL_ANYFORMAT);
//error check
if (surface == NULL)
{
//report error
fprintf(stderr,"Could not set up display surface!\n");
//exit the program
exit(1);
}
FSOUND_Init(44100,32,0);//initialize fmod at 44100 hz, 32 software channels, last
//param is for flags, we won't use any here
FSOUND_STREAM *stream; //make a pointer for the FSOUND_STREAM_LOAD to return to
stream=FSOUND_Stream_Open("filename.mp3", 1, 0, 0);
/*set the stream pointer to our data,
first parameter is the name of our file, second param is the mode in which we're playing
the file, 3rd and 4th parameters are optional offset and length values respectively
if not set they default to 0*/
FSOUND_Stream_Play(FSOUND_FREE, stream);
//repeat
for(;;)
{
//wait for an event
if(SDL_PollEvent(&event)==0)
{
//update screen
SDL_UpdateRect(surface,0,0,0,0);
}
else
{
//event occurred, check for quit
if(event.type==SDL_QUIT) break;
}
}
//cleanup
FSOUND_Stream_Close(stream);//shutdown and close stream
stream=NULL;//make sure we closed it
return(0);
}
As you can see, this is almost exactly like the previous program, most of this is the same window code from before, nothing special, I just stripped out all of the SDL_mixer code and added FMOD code instead. And that's it, FMOD is working. The above code will play .WAV (including the compressed WAV), .MP2, .MP3, .OGG, .MID, .RAW, .MOD, .S3M, .XM, .IT formats via a file stream. All that should be needed is to change the name of the file in FSOUND_Stream_Open. FYI so that you don't make the same mistake, when I started with FMOD I used FMUSIC_LoadSong instead of streaming it, this made a big difference. When you load the song, it loads it and decompresses it into RAM, making for a huge memory footprint just to play one song. Streaming, on the other hand, allows the file to load as it progresses instead of dumping everything into RAM. Loading the entire piece into memory is ideal for sound effects and such that will be played a lot or maybe even short loops that play in the background, but definitely not desirable for a full length song. Again, I apologize for the large delay in updating this thing, but I'm glad I've finished it now. If you have any comments, suggestions, feedback, concern, etc., please e-mail me at oglfreak@hotmail.com. Thanks for reading and I hope that you got something out of this article. Discuss this article in the forums
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