SDL Wiki
(This function is part of SDL_mixer, a separate library from SDL.)

Mix_OpenAudio

Open the default audio device for playback.

Syntax

int Mix_OpenAudio(int frequency, Uint16 format, int channels, int chunksize);

Function Parameters

frequency

the frequency to playback audio at (in Hz).

format

audio format, one of SDL's AUDIO_* values.

channels

number of channels (1 is mono, 2 is stereo, etc).

chunksize

audio buffer size in sample FRAMES (total samples divided by channel count).

Return Value

Returns 0 if successful, -1 on error.

Remarks

An audio device is what generates sound, so the app must open one to make noise.

This function will check if SDL's audio system is initialized, and if not, it will initialize it by calling SDL_Init(SDL_INIT_AUDIO) on your behalf. You are free to (and encouraged to!) initialize it yourself before calling this function, as this gives your program more control over the process.

This function might cover all of an application's needs, but for those that need more flexibility, the more powerful version of this function is Mix_OpenAudioDevice(). This function is equivalent to calling:

Mix_OpenAudioDevice(frequency, format, nchannels, chunksize, NULL,
                    SDL_AUDIO_ALLOW_FREQUENCY_CHANGE |
                    SDL_AUDIO_ALLOW_CHANNELS_CHANGE);

If you aren't particularly concerned with the specifics of the audio device, and your data isn't in a specific format, the values you use here can just be reasonable defaults. SDL_mixer will convert audio data you feed it to the correct format on demand.

That being said, if you have control of your audio data and you know its format ahead of time, you can save CPU time by opening the audio device in that exact format so SDL_mixer does not have to spend time converting anything behind the scenes, and can just pass the data straight through to the hardware. On some platforms, where the hardware only supports specific settings, you might have to be careful to make everything match, but your own data is often easier to control, so aim to open the device for what you need.

The other reason to care about specific formats: if you plan to touch the mix buffer directly (with Mix_SetPostMix, a registered effect, or Mix_HookMusic), you might have code that expects it to be in a specific format, and you should specify that here.

The audio device frequency is specified in Hz; in modern times, 48000 is often a reasonable default.

The audio device format is one of SDL's AUDIO_* constants. AUDIO_S16SYS (16-bit audio) is probably a safe default. More modern systems may prefer AUDIO_F32SYS (32-bit floating point audio).

The audio device channels are generally 1 for mono output, or 2 for stereo, but the brave can try surround sound configs with 4 (quad), 6 (5.1), 7 (6.1) or 8 (7.1).

The audio device's chunk size is the number of sample frames (one sample per frame for mono output, two samples per frame in a stereo setup, etc) that are fed to the device at once. The lower the number, the lower the latency, but you risk dropouts if it gets too low. 2048 is often a reasonable default, but your app might want to experiment with 1024 or 4096.

You may only have one audio device open at a time; if you want to change a setting, you must close the device and reopen it, which is not something you can do seamlessly during playback.

This function does not allow you to select a specific audio device on the system, it always chooses the best default it can on your behalf (which, in many cases, is exactly what you want anyhow). If you must choose a specific device, you can do so with Mix_OpenAudioDevice() instead.

If this function reports success, you are ready to start making noise! Load some audio data and start playing!

The app can use Mix_QuerySpec() to determine the final device settings.

When done with an audio device, probably at the end of the program, the app should dispose of the device with Mix_CloseDevice().

Version

This function is available since SDL_mixer 2.0.0.

Mix_OpenAudioDevice
Mix_CloseDevice

CategoryAPI


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