SDL 3.0
SDL_audio.h File Reference

Audio functionality for the SDL library. More...

#include <SDL3/SDL_stdinc.h>
#include <SDL3/SDL_error.h>
#include <SDL3/SDL_endian.h>
#include <SDL3/SDL_mutex.h>
#include <SDL3/SDL_thread.h>
#include <SDL3/SDL_rwops.h>
#include <SDL3/SDL_begin_code.h>
#include <SDL3/SDL_close_code.h>
+ Include dependency graph for SDL_audio.h:
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Go to the source code of this file.

Data Structures

struct  SDL_AudioSpec
 

Macros

Audio flags
#define SDL_AUDIO_MASK_BITSIZE   (0xFF)
 
#define SDL_AUDIO_MASK_DATATYPE   (1<<8)
 
#define SDL_AUDIO_MASK_ENDIAN   (1<<12)
 
#define SDL_AUDIO_MASK_SIGNED   (1<<15)
 
#define SDL_AUDIO_BITSIZE(x)   (x & SDL_AUDIO_MASK_BITSIZE)
 
#define SDL_AUDIO_ISFLOAT(x)   (x & SDL_AUDIO_MASK_DATATYPE)
 
#define SDL_AUDIO_ISBIGENDIAN(x)   (x & SDL_AUDIO_MASK_ENDIAN)
 
#define SDL_AUDIO_ISSIGNED(x)   (x & SDL_AUDIO_MASK_SIGNED)
 
#define SDL_AUDIO_ISINT(x)   (!SDL_AUDIO_ISFLOAT(x))
 
#define SDL_AUDIO_ISLITTLEENDIAN(x)   (!SDL_AUDIO_ISBIGENDIAN(x))
 
#define SDL_AUDIO_ISUNSIGNED(x)   (!SDL_AUDIO_ISSIGNED(x))
 
Audio format flags

Defaults to LSB byte order.

#define SDL_AUDIO_U8   0x0008
 
#define SDL_AUDIO_S8   0x8008
 
#define SDL_AUDIO_S16LSB   0x8010
 
#define SDL_AUDIO_S16MSB   0x9010
 
#define SDL_AUDIO_S16   SDL_AUDIO_S16LSB
 
int32 support
#define SDL_AUDIO_S32LSB   0x8020
 
#define SDL_AUDIO_S32MSB   0x9020
 
#define SDL_AUDIO_S32   SDL_AUDIO_S32LSB
 
float32 support
#define SDL_AUDIO_F32LSB   0x8120
 
#define SDL_AUDIO_F32MSB   0x9120
 
#define SDL_AUDIO_F32   SDL_AUDIO_F32LSB
 

Typedefs

typedef Uint16 SDL_AudioFormat
 Audio format flags. More...
 

Native audio byte ordering

#define SDL_AUDIO_S16SYS   SDL_AUDIO_S16LSB
 
#define SDL_AUDIO_S32SYS   SDL_AUDIO_S32LSB
 
#define SDL_AUDIO_F32SYS   SDL_AUDIO_F32LSB
 
#define SDL_AUDIO_DEVICE_DEFAULT_OUTPUT   ((SDL_AudioDeviceID) 0xFFFFFFFF)
 
#define SDL_AUDIO_DEVICE_DEFAULT_CAPTURE   ((SDL_AudioDeviceID) 0xFFFFFFFE)
 
typedef Uint32 SDL_AudioDeviceID
 
typedef struct SDL_AudioStream SDL_AudioStream
 

Driver discovery functions

These functions return the list of built in audio drivers, in the order that they are normally initialized by default.

#define SDL_MIX_MAXVOLUME   128
 
typedef void(* SDL_AudioStreamRequestCallback) (SDL_AudioStream *stream, int approx_request, void *userdata)
 
int SDL_GetNumAudioDrivers (void)
 
const char * SDL_GetAudioDriver (int index)
 
const char * SDL_GetCurrentAudioDriver (void)
 
SDL_AudioDeviceIDSDL_GetAudioOutputDevices (int *count)
 
SDL_AudioDeviceIDSDL_GetAudioCaptureDevices (int *count)
 
char * SDL_GetAudioDeviceName (SDL_AudioDeviceID devid)
 
int SDL_GetAudioDeviceFormat (SDL_AudioDeviceID devid, SDL_AudioSpec *spec)
 
SDL_AudioDeviceID SDL_OpenAudioDevice (SDL_AudioDeviceID devid, const SDL_AudioSpec *spec)
 
int SDL_PauseAudioDevice (SDL_AudioDeviceID dev)
 
int SDL_ResumeAudioDevice (SDL_AudioDeviceID dev)
 
SDL_bool SDL_IsAudioDevicePaused (SDL_AudioDeviceID dev)
 
void SDL_CloseAudioDevice (SDL_AudioDeviceID devid)
 
int SDL_BindAudioStreams (SDL_AudioDeviceID devid, SDL_AudioStream **streams, int num_streams)
 
int SDL_BindAudioStream (SDL_AudioDeviceID devid, SDL_AudioStream *stream)
 
void SDL_UnbindAudioStreams (SDL_AudioStream **streams, int num_streams)
 
void SDL_UnbindAudioStream (SDL_AudioStream *stream)
 
SDL_AudioDeviceID SDL_GetAudioStreamBinding (SDL_AudioStream *stream)
 
SDL_AudioStreamSDL_CreateAudioStream (const SDL_AudioSpec *src_spec, const SDL_AudioSpec *dst_spec)
 
int SDL_GetAudioStreamFormat (SDL_AudioStream *stream, SDL_AudioSpec *src_spec, SDL_AudioSpec *dst_spec)
 
int SDL_SetAudioStreamFormat (SDL_AudioStream *stream, const SDL_AudioSpec *src_spec, const SDL_AudioSpec *dst_spec)
 
int SDL_PutAudioStreamData (SDL_AudioStream *stream, const void *buf, int len)
 
int SDL_GetAudioStreamData (SDL_AudioStream *stream, void *buf, int len)
 
int SDL_GetAudioStreamAvailable (SDL_AudioStream *stream)
 
int SDL_FlushAudioStream (SDL_AudioStream *stream)
 
int SDL_ClearAudioStream (SDL_AudioStream *stream)
 
int SDL_LockAudioStream (SDL_AudioStream *stream)
 
int SDL_UnlockAudioStream (SDL_AudioStream *stream)
 
int SDL_SetAudioStreamGetCallback (SDL_AudioStream *stream, SDL_AudioStreamRequestCallback callback, void *userdata)
 
int SDL_SetAudioStreamPutCallback (SDL_AudioStream *stream, SDL_AudioStreamRequestCallback callback, void *userdata)
 
void SDL_DestroyAudioStream (SDL_AudioStream *stream)
 
SDL_AudioStreamSDL_CreateAndBindAudioStream (SDL_AudioDeviceID devid, const SDL_AudioSpec *spec)
 
int SDL_LoadWAV_RW (SDL_RWops *src, SDL_bool freesrc, SDL_AudioSpec *spec, Uint8 **audio_buf, Uint32 *audio_len)
 
int SDL_LoadWAV (const char *path, SDL_AudioSpec *spec, Uint8 **audio_buf, Uint32 *audio_len)
 
int SDL_MixAudioFormat (Uint8 *dst, const Uint8 *src, SDL_AudioFormat format, Uint32 len, int volume)
 
int SDL_ConvertAudioSamples (const SDL_AudioSpec *src_spec, const Uint8 *src_data, int src_len, const SDL_AudioSpec *dst_spec, Uint8 **dst_data, int *dst_len)
 
int SDL_GetSilenceValueForFormat (SDL_AudioFormat format)
 

Detailed Description

Audio functionality for the SDL library.

Definition in file SDL_audio.h.

Macro Definition Documentation

◆ SDL_AUDIO_BITSIZE

#define SDL_AUDIO_BITSIZE (   x)    (x & SDL_AUDIO_MASK_BITSIZE)

Definition at line 86 of file SDL_audio.h.

◆ SDL_AUDIO_DEVICE_DEFAULT_CAPTURE

#define SDL_AUDIO_DEVICE_DEFAULT_CAPTURE   ((SDL_AudioDeviceID) 0xFFFFFFFE)

Definition at line 148 of file SDL_audio.h.

◆ SDL_AUDIO_DEVICE_DEFAULT_OUTPUT

#define SDL_AUDIO_DEVICE_DEFAULT_OUTPUT   ((SDL_AudioDeviceID) 0xFFFFFFFF)

Definition at line 147 of file SDL_audio.h.

◆ SDL_AUDIO_F32

#define SDL_AUDIO_F32   SDL_AUDIO_F32LSB

Definition at line 122 of file SDL_audio.h.

◆ SDL_AUDIO_F32LSB

#define SDL_AUDIO_F32LSB   0x8120

32-bit floating point samples

Definition at line 120 of file SDL_audio.h.

◆ SDL_AUDIO_F32MSB

#define SDL_AUDIO_F32MSB   0x9120

As above, but big-endian byte order

Definition at line 121 of file SDL_audio.h.

◆ SDL_AUDIO_F32SYS

#define SDL_AUDIO_F32SYS   SDL_AUDIO_F32LSB

Definition at line 132 of file SDL_audio.h.

◆ SDL_AUDIO_ISBIGENDIAN

#define SDL_AUDIO_ISBIGENDIAN (   x)    (x & SDL_AUDIO_MASK_ENDIAN)

Definition at line 88 of file SDL_audio.h.

◆ SDL_AUDIO_ISFLOAT

#define SDL_AUDIO_ISFLOAT (   x)    (x & SDL_AUDIO_MASK_DATATYPE)

Definition at line 87 of file SDL_audio.h.

◆ SDL_AUDIO_ISINT

#define SDL_AUDIO_ISINT (   x)    (!SDL_AUDIO_ISFLOAT(x))

Definition at line 90 of file SDL_audio.h.

◆ SDL_AUDIO_ISLITTLEENDIAN

#define SDL_AUDIO_ISLITTLEENDIAN (   x)    (!SDL_AUDIO_ISBIGENDIAN(x))

Definition at line 91 of file SDL_audio.h.

◆ SDL_AUDIO_ISSIGNED

#define SDL_AUDIO_ISSIGNED (   x)    (x & SDL_AUDIO_MASK_SIGNED)

Definition at line 89 of file SDL_audio.h.

◆ SDL_AUDIO_ISUNSIGNED

#define SDL_AUDIO_ISUNSIGNED (   x)    (!SDL_AUDIO_ISSIGNED(x))

Definition at line 92 of file SDL_audio.h.

◆ SDL_AUDIO_MASK_BITSIZE

#define SDL_AUDIO_MASK_BITSIZE   (0xFF)

Definition at line 82 of file SDL_audio.h.

◆ SDL_AUDIO_MASK_DATATYPE

#define SDL_AUDIO_MASK_DATATYPE   (1<<8)

Definition at line 83 of file SDL_audio.h.

◆ SDL_AUDIO_MASK_ENDIAN

#define SDL_AUDIO_MASK_ENDIAN   (1<<12)

Definition at line 84 of file SDL_audio.h.

◆ SDL_AUDIO_MASK_SIGNED

#define SDL_AUDIO_MASK_SIGNED   (1<<15)

Definition at line 85 of file SDL_audio.h.

◆ SDL_AUDIO_S16

#define SDL_AUDIO_S16   SDL_AUDIO_S16LSB

Definition at line 104 of file SDL_audio.h.

◆ SDL_AUDIO_S16LSB

#define SDL_AUDIO_S16LSB   0x8010

Signed 16-bit samples

Definition at line 102 of file SDL_audio.h.

◆ SDL_AUDIO_S16MSB

#define SDL_AUDIO_S16MSB   0x9010

As above, but big-endian byte order

Definition at line 103 of file SDL_audio.h.

◆ SDL_AUDIO_S16SYS

#define SDL_AUDIO_S16SYS   SDL_AUDIO_S16LSB

Definition at line 130 of file SDL_audio.h.

◆ SDL_AUDIO_S32

#define SDL_AUDIO_S32   SDL_AUDIO_S32LSB

Definition at line 113 of file SDL_audio.h.

◆ SDL_AUDIO_S32LSB

#define SDL_AUDIO_S32LSB   0x8020

32-bit integer samples

Definition at line 111 of file SDL_audio.h.

◆ SDL_AUDIO_S32MSB

#define SDL_AUDIO_S32MSB   0x9020

As above, but big-endian byte order

Definition at line 112 of file SDL_audio.h.

◆ SDL_AUDIO_S32SYS

#define SDL_AUDIO_S32SYS   SDL_AUDIO_S32LSB

Definition at line 131 of file SDL_audio.h.

◆ SDL_AUDIO_S8

#define SDL_AUDIO_S8   0x8008

Signed 8-bit samples

Definition at line 101 of file SDL_audio.h.

◆ SDL_AUDIO_U8

#define SDL_AUDIO_U8   0x0008

Unsigned 8-bit samples

Definition at line 100 of file SDL_audio.h.

◆ SDL_MIX_MAXVOLUME

#define SDL_MIX_MAXVOLUME   128

Definition at line 1188 of file SDL_audio.h.

Typedef Documentation

◆ SDL_AudioDeviceID

SDL Audio Device instance IDs.

Definition at line 145 of file SDL_audio.h.

◆ SDL_AudioFormat

Audio format flags.

These are what the 16 bits in SDL_AudioFormat currently mean... (Unspecified bits are always zero).

++-----------------------sample is signed if set
||
||       ++-----------sample is bigendian if set
||       ||
||       ||          ++---sample is float if set
||       ||          ||
||       ||          || +---sample bit size---+
||       ||          || |                     |
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

There are macros in SDL 2.0 and later to query these bits.

Definition at line 75 of file SDL_audio.h.

◆ SDL_AudioStream

Definition at line 169 of file SDL_audio.h.

◆ SDL_AudioStreamRequestCallback

typedef void(* SDL_AudioStreamRequestCallback) (SDL_AudioStream *stream, int approx_request, void *userdata)

A callback that fires when data passes through an SDL_AudioStream.

Apps can (optionally) register a callback with an audio stream that is called when data is added with SDL_PutAudioStreamData, or requested with SDL_GetAudioStreamData. These callbacks may run from any thread, so if you need to protect shared data, you should use SDL_LockAudioStream to serialize access; this lock will be held by before your callback is called, so your callback does not need to manage the lock explicitly.

Parameters
streamThe SDL audio stream associated with this callback.
approx_requestThe approximate amout of data, in bytes, that is requested. This might be slightly overestimated due to buffering or resampling, and may change from call to call anyhow.
userdataAn opaque pointer provided by the app for their personal use.

Definition at line 918 of file SDL_audio.h.

Function Documentation

◆ SDL_BindAudioStream()

int SDL_BindAudioStream ( SDL_AudioDeviceID  devid,
SDL_AudioStream stream 
)

Bind a single audio stream to an audio device.

This is a convenience function, equivalent to calling SDL_BindAudioStreams(devid, &stream, 1).

Parameters
devidan audio device to bind a stream to.
streaman audio stream to bind to a device.
Returns
0 on success, -1 on error; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BindAudioStreams
SDL_UnbindAudioStreams
SDL_UnbindAudioStream
SDL_GetAudioStreamBinding

◆ SDL_BindAudioStreams()

int SDL_BindAudioStreams ( SDL_AudioDeviceID  devid,
SDL_AudioStream **  streams,
int  num_streams 
)

Bind a list of audio streams to an audio device.

Audio data will flow through any bound streams. For an output device, data for all bound streams will be mixed together and fed to the device. For a capture device, a copy of recorded data will be provided to each bound stream.

Audio streams can only be bound to an open device. This operation is atomic–all streams bound in the same call will start processing at the same time, so they can stay in sync. Also: either all streams will be bound or none of them will be.

It is an error to bind an already-bound stream; it must be explicitly unbound first.

Binding a stream to a device will set its output format for output devices, and its input format for capture devices, so they match the device's settings. The caller is welcome to change the other end of the stream's format at any time.

Parameters
devidan audio device to bind a stream to.
streamsan array of audio streams to unbind.
num_streamsNumber streams listed in the streams array.
Returns
0 on success, -1 on error; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BindAudioStreams
SDL_UnbindAudioStreams
SDL_UnbindAudioStream
SDL_GetAudioStreamBinding

◆ SDL_ClearAudioStream()

int SDL_ClearAudioStream ( SDL_AudioStream stream)

Clear any pending data in the stream without converting it

Parameters
streamThe audio stream to clear
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream
SDL_PutAudioStreamData
SDL_GetAudioStreamData
SDL_GetAudioStreamAvailable
SDL_FlushAudioStream
SDL_DestroyAudioStream

◆ SDL_CloseAudioDevice()

void SDL_CloseAudioDevice ( SDL_AudioDeviceID  devid)

Close a previously-opened audio device.

The application should close open audio devices once they are no longer needed.

This function may block briefly while pending audio data is played by the hardware, so that applications don't drop the last buffer of data they supplied if terminating immediately afterwards.

Parameters
devidan audio device id previously returned by SDL_OpenAudioDevice()

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_OpenAudioDevice

◆ SDL_ConvertAudioSamples()

int SDL_ConvertAudioSamples ( const SDL_AudioSpec src_spec,
const Uint8 src_data,
int  src_len,
const SDL_AudioSpec dst_spec,
Uint8 **  dst_data,
int *  dst_len 
)

Convert some audio data of one format to another format.

Please note that this function is for convenience, but should not be used to resample audio in blocks, as it will introduce audio artifacts on the boundaries. You should only use this function if you are converting audio data in its entirety in one call. If you want to convert audio in smaller chunks, use an SDL_AudioStream, which is designed for this situation.

Internally, this function creates and destroys an SDL_AudioStream on each use, so it's also less efficient than using one directly, if you need to convert multiple times.

Parameters
src_specThe format details of the input audio
src_dataThe audio data to be converted
src_lenThe len of src_data
dst_specThe format details of the output audio
dst_dataWill be filled with a pointer to converted audio data, which should be freed with SDL_free(). On error, it will be NULL.
dst_lenWill be filled with the len of dst_data
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream

◆ SDL_CreateAndBindAudioStream()

SDL_AudioStream * SDL_CreateAndBindAudioStream ( SDL_AudioDeviceID  devid,
const SDL_AudioSpec spec 
)

Convenience function to create and bind an audio stream in one step.

This manages the creation of an audio stream, and setting its format correctly to match both the app and the audio device's needs. This is optional, but slightly less cumbersome to set up for a common use case.

The spec parameter represents the app's side of the audio stream. That is, for recording audio, this will be the output format, and for playing audio, this will be the input format. This function will set the other side of the audio stream to the device's format.

Parameters
devidan audio device to bind a stream to. This must be an opened device, and can not be zero.
specthe audio stream's input format
Returns
a bound audio stream on success, ready to use. NULL on error; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BindAudioStreams
SDL_UnbindAudioStreams
SDL_UnbindAudioStream

◆ SDL_CreateAudioStream()

SDL_AudioStream * SDL_CreateAudioStream ( const SDL_AudioSpec src_spec,
const SDL_AudioSpec dst_spec 
)

Create a new audio stream.

Parameters
src_specThe format details of the input audio
dst_specThe format details of the output audio
Returns
0 on success, or -1 on error.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_PutAudioStreamData
SDL_GetAudioStreamData
SDL_GetAudioStreamAvailable
SDL_FlushAudioStream
SDL_ClearAudioStream
SDL_ChangeAudioStreamOutput
SDL_DestroyAudioStream

◆ SDL_DestroyAudioStream()

void SDL_DestroyAudioStream ( SDL_AudioStream stream)

Free an audio stream

Parameters
streamThe audio stream to free

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream
SDL_PutAudioStreamData
SDL_GetAudioStreamData
SDL_GetAudioStreamAvailable
SDL_FlushAudioStream
SDL_ClearAudioStream

◆ SDL_FlushAudioStream()

int SDL_FlushAudioStream ( SDL_AudioStream stream)

Tell the stream that you're done sending data, and anything being buffered should be converted/resampled and made available immediately.

It is legal to add more data to a stream after flushing, but there will be audio gaps in the output. Generally this is intended to signal the end of input, so the complete output becomes available.

Parameters
streamThe audio stream to flush
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream
SDL_PutAudioStreamData
SDL_GetAudioStreamData
SDL_GetAudioStreamAvailable
SDL_ClearAudioStream
SDL_DestroyAudioStream

◆ SDL_GetAudioCaptureDevices()

SDL_AudioDeviceID * SDL_GetAudioCaptureDevices ( int *  count)

Get a list of currently-connected audio capture devices.

This returns of list of available devices that record audio, like a microphone ("capture" devices). If you want devices that play sound, perhaps to speakers or headphones ("output" devices), use SDL_GetAudioOutputDevices() instead.

This only returns a list of physical devices; it will not have any device IDs returned by SDL_OpenAudioDevice().

Parameters
counta pointer filled in with the number of devices returned
Returns
a 0 terminated array of device instance IDs which should be freed with SDL_free(), or NULL on error; call SDL_GetError() for more details.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_OpenAudioDevice
SDL_GetAudioOutputDevices

◆ SDL_GetAudioDeviceFormat()

int SDL_GetAudioDeviceFormat ( SDL_AudioDeviceID  devid,
SDL_AudioSpec spec 
)

Get the current audio format of a specific audio device.

For an opened device, this will report the format the device is currently using. If the device isn't yet opened, this will report the device's preferred format (or a reasonable default if this can't be determined).

You may also specify SDL_AUDIO_DEVICE_DEFAULT_OUTPUT or SDL_AUDIO_DEVICE_DEFAULT_CAPTURE here, which is useful for getting a reasonable recommendation before opening the system-recommended default device.

Parameters
devidthe instance ID of the device to query.
specOn return, will be filled with device details.
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.

◆ SDL_GetAudioDeviceName()

char * SDL_GetAudioDeviceName ( SDL_AudioDeviceID  devid)

Get the human-readable name of a specific audio device.

The string returned by this function is UTF-8 encoded. The caller should call SDL_free on the return value when done with it.

Parameters
devidthe instance ID of the device to query.
Returns
the name of the audio device, or NULL on error.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_GetNumAudioDevices
SDL_GetDefaultAudioInfo

◆ SDL_GetAudioDriver()

const char * SDL_GetAudioDriver ( int  index)

Use this function to get the name of a built in audio driver.

The list of audio drivers is given in the order that they are normally initialized by default; the drivers that seem more reasonable to choose first (as far as the SDL developers believe) are earlier in the list.

The names of drivers are all simple, low-ASCII identifiers, like "alsa", "coreaudio" or "xaudio2". These never have Unicode characters, and are not meant to be proper names.

Parameters
indexthe index of the audio driver; the value ranges from 0 to SDL_GetNumAudioDrivers() - 1
Returns
the name of the audio driver at the requested index, or NULL if an invalid index was specified.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_GetNumAudioDrivers

◆ SDL_GetAudioOutputDevices()

SDL_AudioDeviceID * SDL_GetAudioOutputDevices ( int *  count)

Get a list of currently-connected audio output devices.

This returns of list of available devices that play sound, perhaps to speakers or headphones ("output" devices). If you want devices that record audio, like a microphone ("capture" devices), use SDL_GetAudioCaptureDevices() instead.

This only returns a list of physical devices; it will not have any device IDs returned by SDL_OpenAudioDevice().

Parameters
counta pointer filled in with the number of devices returned
Returns
a 0 terminated array of device instance IDs which should be freed with SDL_free(), or NULL on error; call SDL_GetError() for more details.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_OpenAudioDevice
SDL_GetAudioCaptureDevices

◆ SDL_GetAudioStreamAvailable()

int SDL_GetAudioStreamAvailable ( SDL_AudioStream stream)

Get the number of converted/resampled bytes available.

The stream may be buffering data behind the scenes until it has enough to resample correctly, so this number might be lower than what you expect, or even be zero. Add more data or flush the stream if you need the data now.

If the stream has so much data that it would overflow an int, the return value is clamped to a maximum value, but no queued data is lost; if there are gigabytes of data queued, the app might need to read some of it with SDL_GetAudioStreamData before this function's return value is no longer clamped.

Parameters
streamThe audio stream to query
Returns
the number of converted/resampled bytes available.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream
SDL_PutAudioStreamData
SDL_GetAudioStreamData
SDL_FlushAudioStream
SDL_ClearAudioStream
SDL_DestroyAudioStream

◆ SDL_GetAudioStreamBinding()

SDL_AudioDeviceID SDL_GetAudioStreamBinding ( SDL_AudioStream stream)

Query an audio stream for its currently-bound device.

This reports the audio device that an audio stream is currently bound to.

If not bound, or invalid, this returns zero, which is not a valid device ID.

Parameters
streamthe audio stream to query.
Returns
The bound audio device, or 0 if not bound or invalid.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BindAudioStream
SDL_BindAudioStreams
SDL_UnbindAudioStream
SDL_UnbindAudioStreams

◆ SDL_GetAudioStreamData()

int SDL_GetAudioStreamData ( SDL_AudioStream stream,
void *  buf,
int  len 
)

Get converted/resampled data from the stream.

The input/output data format/channels/samplerate is specified when creating the stream, and can be changed after creation by calling SDL_SetAudioStreamFormat.

Note that any conversion and resampling necessary is done during this call, and SDL_PutAudioStreamData simply queues unconverted data for later. This is different than SDL2, where that work was done while inputting new data to the stream and requesting the output just copied the converted data.

Parameters
streamThe stream the audio is being requested from
bufA buffer to fill with audio data
lenThe maximum number of bytes to fill
Returns
the number of bytes read from the stream, or -1 on error

\threadsafety It is safe to call this function from any thread, but if the stream has a callback set, the caller might need to manage extra locking.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream
SDL_PutAudioStreamData
SDL_GetAudioStreamAvailable
SDL_SetAudioStreamFormat
SDL_FlushAudioStream
SDL_ClearAudioStream
SDL_DestroyAudioStream

◆ SDL_GetAudioStreamFormat()

int SDL_GetAudioStreamFormat ( SDL_AudioStream stream,
SDL_AudioSpec src_spec,
SDL_AudioSpec dst_spec 
)

Query the current format of an audio stream.

Parameters
streamthe SDL_AudioStream to query.
src_specWhere to store the input audio format; ignored if NULL.
dst_specWhere to store the output audio format; ignored if NULL.
Returns
0 on success, or -1 on error.

\threadsafety It is safe to call this function from any thread, as it holds a stream-specific mutex while running.

Since
This function is available since SDL 3.0.0.

◆ SDL_GetCurrentAudioDriver()

const char * SDL_GetCurrentAudioDriver ( void  )

Get the name of the current audio driver.

The returned string points to internal static memory and thus never becomes invalid, even if you quit the audio subsystem and initialize a new driver (although such a case would return a different static string from another call to this function, of course). As such, you should not modify or free the returned string.

Returns
the name of the current audio driver or NULL if no driver has been initialized.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.

◆ SDL_GetNumAudioDrivers()

int SDL_GetNumAudioDrivers ( void  )

Use this function to get the number of built-in audio drivers.

This function returns a hardcoded number. This never returns a negative value; if there are no drivers compiled into this build of SDL, this function returns zero. The presence of a driver in this list does not mean it will function, it just means SDL is capable of interacting with that interface. For example, a build of SDL might have esound support, but if there's no esound server available, SDL's esound driver would fail if used.

By default, SDL tries all drivers, in its preferred order, until one is found to be usable.

Returns
the number of built-in audio drivers.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_GetAudioDriver

◆ SDL_GetSilenceValueForFormat()

int SDL_GetSilenceValueForFormat ( SDL_AudioFormat  format)

Get the appropriate memset value for silencing an audio format.

The value returned by this function can be used as the second argument to memset (or SDL_memset) to set an audio buffer in a specific format to silence.

Parameters
formatthe audio data format to query.
Returns
A byte value that can be passed to memset.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.

◆ SDL_IsAudioDevicePaused()

SDL_bool SDL_IsAudioDevicePaused ( SDL_AudioDeviceID  dev)

Use this function to query if an audio device is paused.

Unlike in SDL2, audio devices start in an unpaused state, since an app has to bind a stream before any audio will flow.

Physical devices can not be paused or unpaused, only logical devices created through SDL_OpenAudioDevice() can be. Physical and invalid device IDs will report themselves as unpaused here.

Parameters
deva device opened by SDL_OpenAudioDevice()
Returns
SDL_TRUE if device is valid and paused, SDL_FALSE otherwise.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_PauseAudioDevice
SDL_ResumeAudioDevice
SDL_IsAudioDevicePaused

◆ SDL_LoadWAV()

int SDL_LoadWAV ( const char *  path,
SDL_AudioSpec spec,
Uint8 **  audio_buf,
Uint32 audio_len 
)

Loads a WAV from a file path.

This is a convenience function that is effectively the same as:

SDL_LoadWAV_RW(SDL_RWFromFile(path, "rb"), 1, spec, audio_buf, audio_len);
int SDL_LoadWAV_RW(SDL_RWops *src, SDL_bool freesrc, SDL_AudioSpec *spec, Uint8 **audio_buf, Uint32 *audio_len)
SDL_RWops * SDL_RWFromFile(const char *file, const char *mode)

Note that in SDL2, this was a preprocessor macro and not a real function.

Parameters
pathThe file path of the WAV file to open.
specA pointer to an SDL_AudioSpec that will be set to the WAVE data's format details on successful return.
audio_bufA pointer filled with the audio data, allocated by the function.
audio_lenA pointer filled with the length of the audio data buffer in bytes
Returns
This function, if successfully called, returns 0. audio_buf will be filled with a pointer to an allocated buffer containing the audio data, and audio_len is filled with the length of that audio buffer in bytes.

This function returns -1 if the .WAV file cannot be opened, uses an unknown data format, or is corrupt; call SDL_GetError() for more information.

When the application is done with the data returned in audio_buf, it should call SDL_free() to dispose of it.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_free
SDL_LoadWAV_RW

◆ SDL_LoadWAV_RW()

int SDL_LoadWAV_RW ( SDL_RWops src,
SDL_bool  freesrc,
SDL_AudioSpec spec,
Uint8 **  audio_buf,
Uint32 audio_len 
)

Load the audio data of a WAVE file into memory.

Loading a WAVE file requires src, spec, audio_buf and audio_len to be valid pointers. The entire data portion of the file is then loaded into memory and decoded if necessary.

Supported formats are RIFF WAVE files with the formats PCM (8, 16, 24, and 32 bits), IEEE Float (32 bits), Microsoft ADPCM and IMA ADPCM (4 bits), and A-law and mu-law (8 bits). Other formats are currently unsupported and cause an error.

If this function succeeds, the return value is zero and the pointer to the audio data allocated by the function is written to audio_buf and its length in bytes to audio_len. The SDL_AudioSpec members freq, channels, and format are set to the values of the audio data in the buffer. The samples member is set to a sane default and all others are set to zero.

It's necessary to use SDL_free() to free the audio data returned in audio_buf when it is no longer used.

Because of the underspecification of the .WAV format, there are many problematic files in the wild that cause issues with strict decoders. To provide compatibility with these files, this decoder is lenient in regards to the truncation of the file, the fact chunk, and the size of the RIFF chunk. The hints SDL_HINT_WAVE_RIFF_CHUNK_SIZE, SDL_HINT_WAVE_TRUNCATION, and SDL_HINT_WAVE_FACT_CHUNK can be used to tune the behavior of the loading process.

Any file that is invalid (due to truncation, corruption, or wrong values in the headers), too big, or unsupported causes an error. Additionally, any critical I/O error from the data source will terminate the loading process with an error. The function returns NULL on error and in all cases (with the exception of src being NULL), an appropriate error message will be set.

It is required that the data source supports seeking.

Example:

SDL_LoadWAV_RW(SDL_RWFromFile("sample.wav", "rb"), 1, &spec, &buf, &len);

Note that the SDL_LoadWAV function does this same thing for you, but in a less messy way:

SDL_LoadWAV("sample.wav", &spec, &buf, &len);
int SDL_LoadWAV(const char *path, SDL_AudioSpec *spec, Uint8 **audio_buf, Uint32 *audio_len)
Parameters
srcThe data source for the WAVE data
freesrcIf SDL_TRUE, calls SDL_RWclose() on src before returning, even in the case of an error
specA pointer to an SDL_AudioSpec that will be set to the WAVE data's format details on successful return
audio_bufA pointer filled with the audio data, allocated by the function
audio_lenA pointer filled with the length of the audio data buffer in bytes
Returns
This function, if successfully called, returns 0. audio_buf will be filled with a pointer to an allocated buffer containing the audio data, and audio_len is filled with the length of that audio buffer in bytes.

This function returns -1 if the .WAV file cannot be opened, uses an unknown data format, or is corrupt; call SDL_GetError() for more information.

When the application is done with the data returned in audio_buf, it should call SDL_free() to dispose of it.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_free
SDL_LoadWAV

◆ SDL_LockAudioStream()

int SDL_LockAudioStream ( SDL_AudioStream stream)

Lock an audio stream for serialized access.

Each SDL_AudioStream has an internal mutex it uses to protect its data structures from threading conflicts. This function allows an app to lock that mutex, which could be useful if registering callbacks on this stream.

One does not need to lock a stream to use in it most cases, as the stream manages this lock internally. However, this lock is held during callbacks, which may run from arbitrary threads at any time, so if an app needs to protect shared data during those callbacks, locking the stream guarantees that the callback is not running while the lock is held.

As this is just a wrapper over SDL_LockMutex for an internal lock, it has all the same attributes (recursive locks are allowed, etc).

Parameters
streamThe audio stream to lock.
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_UnlockAudioStream
SDL_SetAudioStreamPutCallback
SDL_SetAudioStreamGetCallback

◆ SDL_MixAudioFormat()

int SDL_MixAudioFormat ( Uint8 dst,
const Uint8 src,
SDL_AudioFormat  format,
Uint32  len,
int  volume 
)

Mix audio data in a specified format.

This takes an audio buffer src of len bytes of format data and mixes it into dst, performing addition, volume adjustment, and overflow clipping. The buffer pointed to by dst must also be len bytes of format data.

This is provided for convenience – you can mix your own audio data.

Do not use this function for mixing together more than two streams of sample data. The output from repeated application of this function may be distorted by clipping, because there is no accumulator with greater range than the input (not to mention this being an inefficient way of doing it).

It is a common misconception that this function is required to write audio data to an output stream in an audio callback. While you can do that, SDL_MixAudioFormat() is really only needed when you're mixing a single audio stream with a volume adjustment.

Parameters
dstthe destination for the mixed audio
srcthe source audio buffer to be mixed
formatthe SDL_AudioFormat structure representing the desired audio format
lenthe length of the audio buffer in bytes
volumeranges from 0 - 128, and should be set to SDL_MIX_MAXVOLUME for full audio volume
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.

◆ SDL_OpenAudioDevice()

SDL_AudioDeviceID SDL_OpenAudioDevice ( SDL_AudioDeviceID  devid,
const SDL_AudioSpec spec 
)

Open a specific audio device.

You can open both output and capture devices through this function. Output devices will take data from bound audio streams, mix it, and send it to the hardware. Capture devices will feed any bound audio streams with a copy of any incoming data.

An opened audio device starts out with no audio streams bound. To start audio playing, bind a stream and supply audio data to it. Unlike SDL2, there is no audio callback; you only bind audio streams and make sure they have data flowing into them (although, as an optional feature, each audio stream may have its own callback, which can be used to simulate SDL2's semantics).

If you don't care about opening a specific device, pass a devid of either SDL_AUDIO_DEVICE_DEFAULT_OUTPUT or SDL_AUDIO_DEVICE_DEFAULT_CAPTURE. In this case, SDL will try to pick the most reasonable default, and may also switch between physical devices seamlessly later, if the most reasonable default changes during the lifetime of this opened device (user changed the default in the OS's system preferences, the default got unplugged so the system jumped to a new default, the user plugged in headphones on a mobile device, etc). Unless you have a good reason to choose a specific device, this is probably what you want.

You may request a specific format for the audio device, but there is no promise the device will honor that request for several reasons. As such, it's only meant to be a hint as to what data your app will provide. Audio streams will accept data in whatever format you specify and manage conversion for you as appropriate. SDL_GetAudioDeviceFormat can tell you the preferred format for the device before opening and the actual format the device is using after opening.

It's legal to open the same device ID more than once; each successful open will generate a new logical SDL_AudioDeviceID that is managed separately from others on the same physical device. This allows libraries to open a device separately from the main app and bind its own streams without conflicting.

It is also legal to open a device ID returned by a previous call to this function; doing so just creates another logical device on the same physical device. This may be useful for making logical groupings of audio streams.

This function returns the opened device ID on success. This is a new, unique SDL_AudioDeviceID that represents a logical device.

Some backends might offer arbitrary devices (for example, a networked audio protocol that can connect to an arbitrary server). For these, as a change from SDL2, you should open a default device ID and use an SDL hint to specify the target if you care, or otherwise let the backend figure out a reasonable default. Most backends don't offer anything like this, and often this would be an end user setting an environment variable for their custom need, and not something an application should specifically manage.

When done with an audio device, possibly at the end of the app's life, one should call SDL_CloseAudioDevice() on the returned device id.

Parameters
devidthe device instance id to open, or SDL_AUDIO_DEVICE_DEFAULT_OUTPUT or SDL_AUDIO_DEVICE_DEFAULT_CAPTURE for the most reasonable default device.
specthe requested device configuration. Can be NULL to use reasonable defaults.
Returns
The device ID on success, 0 on error; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_CloseAudioDevice
SDL_GetAudioDeviceFormat

◆ SDL_PauseAudioDevice()

int SDL_PauseAudioDevice ( SDL_AudioDeviceID  dev)

Use this function to pause audio playback on a specified device.

This function pauses audio processing for a given device. Any bound audio streams will not progress, and no audio will be generated. Pausing one device does not prevent other unpaused devices from running.

Unlike in SDL2, audio devices start in an unpaused state, since an app has to bind a stream before any audio will flow. Pausing a paused device is a legal no-op.

Pausing a device can be useful to halt all audio without unbinding all the audio streams. This might be useful while a game is paused, or a level is loading, etc.

Physical devices can not be paused or unpaused, only logical devices created through SDL_OpenAudioDevice() can be.

Parameters
deva device opened by SDL_OpenAudioDevice()
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_ResumeAudioDevice
SDL_IsAudioDevicePaused

◆ SDL_PutAudioStreamData()

int SDL_PutAudioStreamData ( SDL_AudioStream stream,
const void *  buf,
int  len 
)

Add data to be converted/resampled to the stream.

This data must match the format/channels/samplerate specified in the latest call to SDL_SetAudioStreamFormat, or the format specified when creating the stream if it hasn't been changed.

Note that this call simply queues unconverted data for later. This is different than SDL2, where data was converted during the Put call and the Get call would just dequeue the previously-converted data.

Parameters
streamThe stream the audio data is being added to
bufA pointer to the audio data to add
lenThe number of bytes to write to the stream
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread, but if the stream has a callback set, the caller might need to manage extra locking.

Since
This function is available since SDL 3.0.0.
See also
SDL_CreateAudioStream
SDL_GetAudioStreamData
SDL_GetAudioStreamAvailable
SDL_FlushAudioStream
SDL_ClearAudioStream
SDL_DestroyAudioStream

◆ SDL_ResumeAudioDevice()

int SDL_ResumeAudioDevice ( SDL_AudioDeviceID  dev)

Use this function to unpause audio playback on a specified device.

This function unpauses audio processing for a given device that has previously been paused with SDL_PauseAudioDevice(). Once unpaused, any bound audio streams will begin to progress again, and audio can be generated.

Unlike in SDL2, audio devices start in an unpaused state, since an app has to bind a stream before any audio will flow. Unpausing an unpaused device is a legal no-op.

Physical devices can not be paused or unpaused, only logical devices created through SDL_OpenAudioDevice() can be.

Parameters
deva device opened by SDL_OpenAudioDevice()
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_ResumeAudioDevice
SDL_IsAudioDevicePaused

◆ SDL_SetAudioStreamFormat()

int SDL_SetAudioStreamFormat ( SDL_AudioStream stream,
const SDL_AudioSpec src_spec,
const SDL_AudioSpec dst_spec 
)

Change the input and output formats of an audio stream.

Future calls to and SDL_GetAudioStreamAvailable and SDL_GetAudioStreamData will reflect the new format, and future calls to SDL_PutAudioStreamData must provide data in the new input formats.

Parameters
streamThe stream the format is being changed
src_specThe new format of the audio input; if NULL, it is not changed.
dst_specThe new format of the audio output; if NULL, it is not changed.
Returns
0 on success, or -1 on error.

\threadsafety It is safe to call this function from any thread, as it holds a stream-specific mutex while running.

Since
This function is available since SDL 3.0.0.
See also
SDL_GetAudioStreamFormat
SDL_PutAudioStreamData
SDL_GetAudioStreamData
SDL_GetAudioStreamAvailable

◆ SDL_SetAudioStreamGetCallback()

int SDL_SetAudioStreamGetCallback ( SDL_AudioStream stream,
SDL_AudioStreamRequestCallback  callback,
void *  userdata 
)

Set a callback that runs when data is requested from an audio stream.

This callback is called before data is obtained from the stream, giving the callback the chance to add more on-demand.

The callback can (optionally) call SDL_PutAudioStreamData() to add more audio to the stream during this call; if needed, the request that triggered this callback will obtain the new data immediately.

The callback's approx_request argument is roughly how many bytes of unconverted data (in the stream's input format) is needed by the caller, although this may overestimate a little for safety. This takes into account how much is already in the stream and only asks for any extra necessary to resolve the request, which means the callback may be asked for zero bytes, and a different amount on each call.

The callback is not required to supply exact amounts; it is allowed to supply too much or too little or none at all. The caller will get what's available, up to the amount they requested, regardless of this callback's outcome.

Clearing or flushing an audio stream does not call this callback.

This function obtains the stream's lock, which means any existing callback (get or put) in progress will finish running before setting the new callback.

Setting a NULL function turns off the callback.

Parameters
streamthe audio stream to set the new callback on.
callbackthe new callback function to call when data is added to the stream.
userdataan opaque pointer provided to the callback for its own personal use.
Returns
0 on success, -1 on error. This only fails if stream is NULL.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_SetAudioStreamPutCallback

◆ SDL_SetAudioStreamPutCallback()

int SDL_SetAudioStreamPutCallback ( SDL_AudioStream stream,
SDL_AudioStreamRequestCallback  callback,
void *  userdata 
)

Set a callback that runs when data is added to an audio stream.

This callback is called after the data is added to the stream, giving the callback the chance to obtain it immediately.

The callback can (optionally) call SDL_GetAudioStreamData() to obtain audio from the stream during this call.

The callback's approx_request argument is how many bytes of converted data (in the stream's output format) was provided by the caller, although this may underestimate a little for safety. This value might be less than what is currently available in the stream, if data was already there, and might be less than the caller provided if the stream needs to keep a buffer to aid in resampling. Which means the callback may be provided with zero bytes, and a different amount on each call.

The callback may call SDL_GetAudioStreamAvailable to see the total amount currently available to read from the stream, instead of the total provided by the current call.

The callback is not required to obtain all data. It is allowed to read less or none at all. Anything not read now simply remains in the stream for later access.

Clearing or flushing an audio stream does not call this callback.

This function obtains the stream's lock, which means any existing callback (get or put) in progress will finish running before setting the new callback.

Setting a NULL function turns off the callback.

Parameters
streamthe audio stream to set the new callback on.
callbackthe new callback function to call when data is added to the stream.
userdataan opaque pointer provided to the callback for its own personal use.
Returns
0 on success, -1 on error. This only fails if stream is NULL.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_SetAudioStreamGetCallback

◆ SDL_UnbindAudioStream()

void SDL_UnbindAudioStream ( SDL_AudioStream stream)

Unbind a single audio stream from its audio device.

This is a convenience function, equivalent to calling SDL_UnbindAudioStreams(&stream, 1).

Parameters
streaman audio stream to unbind from a device.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BindAudioStream
SDL_BindAudioStreams
SDL_UnbindAudioStreams
SDL_GetAudioStreamBinding

◆ SDL_UnbindAudioStreams()

void SDL_UnbindAudioStreams ( SDL_AudioStream **  streams,
int  num_streams 
)

Unbind a list of audio streams from their audio devices.

The streams being unbound do not all have to be on the same device. All streams on the same device will be unbound atomically (data will stop flowing through them all unbound streams on the same device at the same time).

Unbinding a stream that isn't bound to a device is a legal no-op.

Parameters
streamsan array of audio streams to unbind.
num_streamsNumber streams listed in the streams array.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BindAudioStreams
SDL_BindAudioStream
SDL_UnbindAudioStream
SDL_GetAudioStreamBinding

◆ SDL_UnlockAudioStream()

int SDL_UnlockAudioStream ( SDL_AudioStream stream)

Unlock an audio stream for serialized access.

This unlocks an audio stream after a call to SDL_LockAudioStream.

Parameters
streamThe audio stream to unlock.
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.

\threadsafety You should only call this from the same thread that previously called SDL_LockAudioStream.

Since
This function is available since SDL 3.0.0.
See also
SDL_LockAudioStream
SDL_SetAudioStreamPutCallback
SDL_SetAudioStreamGetCallback