Audio format flags.

These are what the 16 bits in 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 templates in SDL 2.0 and later to query these bits.

This procedure is called when the audio device needs more data.

userdata An application-specific parameter saved in AudioSpec object.

stream A pointer to the audio data buffer.

len The length of that buffer in bytes.

Once the callback returns, the buffer will no longer be valid. Stereo samples are stored in a LRLRLR ordering.

You can choose to avoid callbacks and use queueAudio() instead, if you like. Just open your audio device with a nil callback.

A structure to hold a set of audio conversion filters and buffers.

This structure is 84 bytes on 32-bit architectures, make sure GCC doesn't pad it out to 88 bytes to guarantee ABI compatibility between compilers. The next time we rev the ABI, make sure to size the ints and add padding.

SDL Audio Device IDs.

A successful call to openAudio() is always device id 1, and legacy SDL audio APIs assume you want this device ID. openAudioDevice() calls always returns devices >= 2 on success. The legacy calls are good both for backwards compatibility and when you don't care about multiple, specific, or capture devices.

Driver discovery procedures.

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

Driver discovery procedures.

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

Initialization.

Internal: These procedures are used internally, and should not be used unless you have a specific need to specify the audio driver you want to use. You should normally use init() or initSubSystem().

Cleanup.

Internal: These procedures are used internally, and should not be used unless you have a specific need to specify the audio driver you want to use. You should normally use init() or initSubSystem().

This procedure opens the audio device with the desired parameters, and returns 0 if successful, placing the actual hardware parameters in the object pointed to by obtained. If obtained is nil, the audio data passed to the callback procedure will be guaranteed to be in the requested format, and will be automatically converted to the hardware audio format if necessary. This procedure returns -1 if it failed to open the audio device, or couldn't set up the audio thread.

When filling in the desired audio spec object,

• desired.freq should be the desired audio frequency in samples-per- second.
• desired.format should be the desired audio format.

• desired.samples is the desired size of the audio buffer, in samples. This number should be a power of two, and may be adjusted by the audio driver to a value more suitable for the hardware. Good values seem to range between 512 and 8096 inclusive, depending on the application and CPU speed. Smaller values yield faster response time, but can lead to underflow if the application is doing heavy processing and cannot fill the audio buffer in time. A stereo sample consists of both right and left channels in LR ordering.

  Note that the number of samples is directly related to time by the following formula:

  ms = (samples*1000)/freq

• desired.size is the size in bytes of the audio buffer, and is calculated by openAudio().
• desired.silence is the value used to set the buffer to silence, and is calculated by openAudio().
• desired.callback should be set to a procedure that will be called when the audio device is ready for more data. It is passed a pointer to the audio buffer, and the length in bytes of the audio buffer. This procedure usually runs in a separate thread, and so you should protect data structures that it accesses by calling lockAudio() and unlockAudio() in your code. Alternately, you may pass a nil pointer here, and call queueAudio() with some frequency, to queue more audio samples to be played.
• desired.userdata is passed as the first parameter to your callback procedure. If you passed a nil callback, this value is ignored.

The audio device starts out playing silence when it's opened, and should be enabled for playing by calling pauseAudio(0) when you are ready for your audio callback procedure to be called. Since the audio driver may modify the requested size of the audio buffer, you should allocate any local mixing buffers after you open the audio device.

Get the number of available devices exposed by the current driver.

Only valid after a successfully initializing the audio subsystem. Returns -1 if an explicit list of devices can't be determined; this is not an error. For example, if SDL is set up to talk to a remote audio server, it can't list every one available on the Internet, but it will still allow a specific host to be specified to openAudioDevice().

In many common cases, when this procedure returns a value <= 0, it can still successfully open the default device (nil for first argument of openAudioDevice()).

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

Must be a value between 0 and (number of audio devices-1). Only valid after a successfully initializing the audio subsystem. The values returned by this procedure reflect the latest call to getNumAudioDevices(); recall that procedure to redetect available hardware.

The string returned by this procedure is UTF-8 encoded, read-only, and managed internally. You are not to free it. If you need to keep the string for any length of time, you should make your own copy of it, as it will be invalid next time any of several other SDL prodedures is called.

Open a specific audio device.

Passing in a device name of nil requests the most reasonable default (and is equivalent to calling openAudio()).

The device name is a UTF-8 string reported by getAudioDeviceName(), but some drivers allow arbitrary and driver-specific strings, such as a hostname/IP address for a remote audio server, or a filename in the diskaudio driver.

Return 0 on error, a valid device ID that is >= 2 on success.

openAudio(), unlike this procedure, always acts on device ID 1.

Pause audio procedures.

These procedures pause and unpause the audio callback processing. They should be called with a parameter of 0 after opening the audio device to start playing sound. This is so you can safely initialize data for your callback procedure after opening the audio device. Silence will be written to the audio device during the pause.

Pause audio procedures.

These procedures pause and unpause the audio callback processing. They should be called with a parameter of 0 after opening the audio device to start playing sound. This is so you can safely initialize data for your callback procedure after opening the audio device. Silence will be written to the audio device during the pause.

loadWAV_RW(rwFromFile("sample.wav", "rb"), 1, ...)

If this procedure succeeds, it returns the given AudioSpec, filled with the audio data format of the wave data, and sets audio_buf[] to a malloc()'d buffer containing the audio data, and sets audio_len[] to the length of that audio buffer, in bytes. You need to free the audio buffer with freeWAV() when you are done with it.

This procedure returns nil and sets the SDL error message if the wave file cannot be opened, uses an unknown data format, or is corrupt. Currently raw and MS-ADPCM WAVE files are supported.

This procedure takes a source format and rate and a destination format and rate, and initializes the cvt object with information needed by convertAudio() to convert a buffer of audio data from one format to the other.

Return -1 if the format conversion is not supported, 0 if there's no conversion needed, or 1 if the audio filter is set up.

Once you have initialized the cvt object using buildAudioCVT(), created an audio buffer cvt.buf, and filled it with cvt.len bytes of audio data in the source format, this procedure will convert it in-place to the desired format.

The data conversion may expand the size of the audio data, so the buffer cvt.buf should be allocated after the cvt object is initialized by buildAudioCVT(), and should be cvt.len*cvt.len_mult bytes long.

Queue more audio on non-callback devices.

SDL offers two ways to feed audio to the device: you can either supply a callback that SDL triggers with some frequency to obtain more audio (pull method), or you can supply no callback, and then SDL will expect you to supply data at regular intervals (push method) with this procedure.

There are no limits on the amount of data you can queue, short of exhaustion of address space. Queued data will drain to the device as necessary without further intervention from you. If the device needs audio but there is not enough queued, it will play silence to make up the difference. This means you will have skips in your audio playback if you aren't routinely queueing sufficient data.

This procedure copies the supplied data, so you are safe to free it when the procedure returns. This procedure is thread-safe, but queueing to the same device from two threads at once does not promise which buffer will be queued first.

You may not queue audio on a device that is using an application-supplied callback; doing so returns an error. You have to use the audio callback or queue audio with this procedure, but not both.

You should not call lockAudio() on the device before queueing; SDL handles locking internally for this procedure.

dev The device ID to which we will queue audio.

data The data to queue to the device for later playback.

len The number of bytes (not samples!) to which (data) points.

Return 0 on success, -1 on error.

See also:

getQueuedAudioSize()

clearQueuedAudio()

Get the number of bytes of still-queued audio.

This is the number of bytes that have been queued for playback with queueAudio(), but have not yet been sent to the hardware.

Once we've sent it to the hardware, this procedure can not decide the exact byte boundary of what has been played. It's possible that we just gave the hardware several kilobytes right before you called this procedure, but it hasn't played any of it yet, or maybe half of it, etc.

You may not queue audio on a device that is using an application-supplied callback; calling this procedure on such a device always returns 0. You have to use the audio callback or queue audio with queueAudio(), but not both.

You should not call lockAudio() on the device before querying; SDL handles locking internally for this procedure.

dev The device ID of which we will query queued audio size.

Return number of bytes (not samples!) of queued audio.

See also:

queueAudio()

clearQueuedAudio()

Drop any queued audio data waiting to be sent to the hardware.

Immediately after this call, getQueuedAudioSize() will return 0 and the hardware will start playing silence if more audio isn't queued.

This will not prevent playback of queued audio that's already been sent to the hardware, as we can not undo that, so expect there to be some fraction of a second of audio that might still be heard. This can be useful if you want to, say, drop any pending music during a level change in your game.

You may not queue audio on a device that is using an application-supplied callback; calling this procedure on such a device is always a no-op. You have to use the audio callback or queue audio with queueAudio(), but not both.

You should not call lockAudio() on the device before clearing the queue; SDL handles locking internally for this procedure.

This procedure always succeeds and thus returns nothing.

dev The device ID of which to clear the audio queue.

See also:

queueAudio()

getQueuedAudioSize()

Audio lock procedure.

The lock manipulated by these procedures protects the callback procedure. During a lockAudio()/unlockAudio() pair, you can be guaranteed that the callback procedure is not running. Do not call these from the callback procedure or you will cause deadlock.

Audio lock procedure.

The lock manipulated by these procedures protects the callback procedure. During a lockAudio()/unlockAudio() pair, you can be guaranteed that the callback procedure is not running. Do not call these from the callback procedure or you will cause deadlock.

Audio unlock procedure.

The lock manipulated by these procedures protects the callback procedure. During a lockAudio()/unlockAudio() pair, you can be guaranteed that the callback procedure is not running. Do not call these from the callback procedure or you will cause deadlock.

Audio unlock procedure.

The lock manipulated by these procedures protects the callback procedure. During a lockAudio()/unlockAudio() pair, you can be guaranteed that the callback procedure is not running. Do not call these from the callback procedure or you will cause deadlock.

Loads a WAV from a file.

Compatibility convenience template.