SDL2::audio - SDL Audio Functions
use SDL2::FFI qw[:atomic]; SDL_assert( 1 == 1 ); my $test = 'nope'; SDL_assert( sub { warn 'testing'; my $retval = $test eq "blah"; $test = "blah"; $retval; } );
Audio functions and data types.
These functions may be imported by name or with the :audio tag.
:audio
Returns the number of built-in audio drivers.
SDL_GetAudioDriver( ... )
Returns the audio driver at the given index. They are listed in the order they are normally initialized by default.
for my $index (0 .. SDL_GetNumAudioDrivers() - 1) { printf "[%d] %s\n", $index, SDL_GetAudioDriver($index); }
Expected parameters include:
index
Returns the name as a string.
SDL_AudioInit( ... )
Initialize a particular audio driver.
my $ok = SDL_AudioInit( 'disk' );
This function is 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 SDL_Init( ... ) or SDL_InitSubSystem( ... ).
SDL_Init( ... )
SDL_InitSubSystem( ... )
name
Returns 0 on success. Check SDL_GetError( ) for more information.
0
SDL_GetError( )
SDL_AudioQuit( )
Closes the current audio driver.
SDL_AudioQuit( );
SDL_GetCurrentAudioDriver( )
Get the name of the current audio driver.
my $driver = SDL_GetCurrentAudioDriver( );
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.
SDL_OpenAudio( ... )
This function is a legacy means of opening the audio device.
This function remains for compatibility with SDL 1.2, but also because it's slightly easier to use than the new functions in SDL 2.0. The new, more powerful, and preferred way to do this is SDL_OpenAudioDevice().
This function is roughly equivalent to:
SDL_OpenAudioDevice(undef, 0, $desired, $obtained, SDL_AUDIO_ALLOW_ANY_CHANGE);
With two notable exceptions:
obtained
desired
SDL_OpenAudioDevice( ... )
This function opens the audio device with the desired parameters, and returns 0 if successful, placing the actual hardware parameters in the structure pointed to by obtained.
If obtained is NULL, the audio data passed to the callback function will be guaranteed to be in the requested format, and will be automatically converted to the actual hardware audio format if necessary. If obtained is NULL, desired will have fields modified.
This function returns a negative error code on failure to open the audio device or failure to set up the audio thread; call SDL_GetError( ) for more information.
SDL_GetNumAudioDevices( ... )
Get the number of built-in audio devices.
my $num = SDL_GetNumberAudioDevices( );
This function is only valid after successfully initializing the audio subsystem.
Note that audio capture support is not implemented as of SDL 2.0.4, so the iscapture parameter is for future expansion and should always be zero for now.
iscapture
This function will return -1 if an explicit list of devices can't be determined. Returning -1 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 in SDL_OpenAudioDevice( ... ).
-1
In many common cases, when this function returns a value <= 0, it can still successfully open the default device (NULL for first argument of SDL_OpenAudioDevice( ... )).
This function may trigger a complete redetect of available hardware. It should not be called for each iteration of a loop, but rather once at the start of a loop:
# Don't do this: for (my $i = 0; $i < SDL_GetNumAudioDevices(0); $i++) { ... } # do this instead: my $count = SDL_GetNumAudioDevices(0); for (my $i = 0; $i < $count; ++$i) { do_something_here(); }
Returns the number of available devices exposed by the current driver or -1 if an explicit list of devices can't be determined. A return value of -1 does not necessarily mean an error condition.
SDL_GetAudioDeviceName( ... )
Get the human-readable name of a specific audio device.
This function is only valid after successfully initializing the audio subsystem. The values returned by this function reflect the latest call to SDL_GetNumAudioDevices( ... ); re-call that function to redetect available hardware.
The string returned by this function 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 functions are called.
SDL_GetNumAudioDevices( ) - 1
Returns the name of the audio device at the requested index, or NULL on error.
SDL_GetAudioDeviceSpec( ... )
Get the preferred audio format of a specific audio device.
This function is only valid after a successfully initializing the audio subsystem. The values returned by this function reflect the latest call to SDL_GetNumAudioDevices( ); re-call that function to redetect available hardware.
SDL_GetNumAudioDevices( )
spec will be filled with the sample rate, sample format, and channel count. All other values in the structure are filled with 0. When the supported struct members are 0, SDL was unable to get the property from the backend.
spec
Returns 0 on success, nonzero on error.
Open a specific audio device.
SDL_OpenAudio( ), unlike this function, always acts on device ID 1. As such, this function will never return a 1 so as not to conflict with the legacy function.
SDL_OpenAudio( )
Please note that SDL 2.0 before 2.0.5 did not support recording; as such, this function would fail if `iscapture` was not zero. Starting with SDL 2.0.5, recording is implemented and this value can be non-zero.
Passing in a device name of NULL requests the most reasonable default (and is equivalent to what SDL_OpenAudio( ) does to choose a device). The device name is a UTF-8 string reported by SDL_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.
device
SDL_GetAudioDeviceName( )
When filling in the desired audio spec structure:
desired->freq
desired->format
desired->samples
ms = (sampleframes*1000)/freq
desired->size
SDL_OpenAudioDevice( )
desired->silence
desired->callback
SDL_LockAudioDevice( )
SDL_UnlockAudioDevice( )
SDL_QueueAudio( )
SDL_DequeueAudio( )
desired->userdata
allowed_changes can have the following flags OR'd together:
allowed_changes
SDL_AUDIO_ALLOW_FREQUENCY_CHANGE
SDL_AUDIO_ALLOW_FORMAT_CHANGE
SDL_AUDIO_ALLOW_CHANNELS_CHANGE
SDL_AUDIO_ALLOW_ANY_CHANGE
These flags specify how SDL should behave when a device cannot offer a specific feature. If the application requests a feature that the hardware doesn't offer, SDL will always try to get the closest equivalent.
For example, if you ask for float32 audio format, but the sound card only supports int16, SDL will set the hardware to int16. If you had set SDL_AUDIO_ALLOW_FORMAT_CHANGE, SDL will change the format in the obtained structure. If that flag was not set, SDL will prepare to convert your callback's float32 audio to int16 before feeding it to the hardware and will keep the originally requested format in the obtained structure.
If your application can only handle one specific data format, pass a zero for allowed_changes and let SDL transparently handle any differences.
An opened audio device starts out paused, and should be enabled for playing by calling SDL_PauseAudioDevice($devid, 0) when you are ready for your audio callback function to be called. Since the audio driver may modify the requested size of the audio buffer, you should allocate any local mixing buffers after you open the audio device.
SDL_PauseAudioDevice($devid, 0)
The audio callback runs in a separate thread in most cases; you can prevent race conditions between your callback and other threads without fully pausing playback with SDL_LockAudioDevice( ). For more information about the callback, see SDL_AudioSpec.
Returns a valid device ID that is > 0 on success or 0 on failure; call SDL_GetError( ) for more information.
SDL_GetAudioStatus( )
Get the current audio status.
Returns an SDL_AudioStatus.
SDL_AudioStatus
SDL_GetAudioDeviceStatus( ... )
Get the current audio status of a particular audio device.
dev
SDL_AudioDeviceID
SDL_PauseAudio( ... )
Pause and unpause audio callback processing.
This function 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 function after opening the audio device. Silence will be written to the audio device during the pause.
pause_on
SDL_PauseAudioDevice( ... )
Pause the audio callback processing of a particular device.
SDL_LoadWAV_RW( ... )
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.
src
audio_buf
audio_len
If freesrc is non-zero, the data source gets automatically closed and freed before the function returns.
freesrc
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 pointer returned by it is equal to spec 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 SDL2::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.
freq
channels
format
samples
It's necessary to use SDL_FreeWAV( ) to free the audio data returned in audio_buf when it is no longer used.
SDL_FreeWAV( )
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.
SDL_HINT_WAVE_RIFF_CHUNK_SIZE
SDL_HINT_WAVE_TRUNCATION
SDL_HINT_WAVE_FACT_CHUNK
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 SDL_LoadWAV( ... ) does this same thing for you, but in a less messy way:
SDL_LoadWAV( ... )
SDL_LoadWAV("sample.wav", $spec, $buf, $len);
This function, if successfully called, returns spec, which will be filled with the audio data format of the wave source data. 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 NULL 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_FreeWAV( ) to dispose of it.
Loads a .WAV from a file.
file
This function is a compatibility convenience function that wraps SDL_LoadWAV_RW( ... ). See that function for return value information.
SDL_FreeWAV( ... )
Free data previously allocated with SDL_LoadWAV( ... ) or SDL_LoadWAV_RW( ... ).
After a WAVE file has been opened with SDL_LoadWAV( ... ) or SDL_LoadWAV_RW( ... ) its data can eventually be freed with SDL_FreeWAV( ... ). It is safe to call this function with a NULL pointer.
SDL_BuildAudioCVT( ... )
Initialize an SDL_AudioCVT structure for conversion.
Before an SDL_AudioCVT structure can be used to convert audio data it must be initialized with source and destination information.
This function will zero out every field of the SDL_AudioCVT, so it must be called before the application fills in the final buffer information.
Once this function has returned successfully, and reported that a conversion is necessary, the application fills in the rest of the fields in SDL_AudioCVT, now that it knows how large a buffer it needs to allocate, and then can call SDL_ConvertAudio() to complete the conversion.
cvt
src_format
src_channels
src_rate
dst_format
dst_channels
dst_rate
Returns 1 if the audio filter is prepared, 0 if no conversion is needed, or a negative error code on failure; call SDL_GetError( ) for more information.
1
SDL_ConvertAudio( ... )
Convert audio data to a desired audio format.
This function does the actual audio data conversion, after the application has called SDL_BuildAudioCVT( ... ) to prepare the conversion information and then filled in the buffer details.
Once the application has initialized the cvt structure using SDL_BuildAudioCVT( ... ), allocated an audio buffer and filled it with audio data in the source format, this function will convert the buffer, in-place, to the desired format.
The data conversion may go through several passes; any given pass may possibly temporarily increase the size of the data. For example, SDL might expand 16-bit data to 32 bits before resampling to a lower frequency, shrinking the data size after having grown it briefly. Since the supplied buffer will be both the source and destination, converting as necessary in-place, the application must allocate a buffer that will fully contain the data during its largest conversion pass. After SDL_BuildAudioCVT( ... ) returns, the application should set the $cvt->len field to the size, in bytes, of the source data, and allocate a buffer that is cvt->len * cvt->len_mult bytes long for the buf field.
$cvt->len
cvt->len * cvt->len_mult
buf
The source data should be copied into this buffer before the call to SDL_ConvertAudio( ... ). Upon successful return, this buffer will contain the converted audio, and cvt->len_cvt will be the size of the converted data, in bytes. Any bytes in the buffer past cvt->len_cvt are undefined once this function returns.
cvt->len_cvt
Returns 0 if the conversion was completed successfully or a negative error code on failure; call SDL_GetError( ) for more information.
SDL_NewAudioStream( ... )
Create a new audio stream.
Returns a SDL2::AudioStream on success.
SDL_AudioStreamPut( ... )
Add data to be converted/resampled to the stream.
stream
len
Returns 0 on success, or -1 on error.
SDL_AudioStreamGet( ... )
Get converted/resampled data from the stream
Returns the number of bytes read from the stream, or -1 on error.
SDL_AudioStreamAvailable( ... )
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.
SDL_AudioStreamFlush( ... )
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.
SDL_AudioStreamClear( ... )
Clear any pending data in the stream without converting it.
SDL_FreeAudioStream( ... )
Free an audio stream.
SDL_MixAudio( ... )
This function is a legacy means of mixing audio.
This function is equivalent to calling
SDL_MixAudioFormat( $dst, $src, $format, $len, $volume );
where $format is the obtained format of the audio device from the legacy SDL_OpenAudio( ... ) function.
$format
dst
volume
128
SDL_MIX_MAXVOLUME
SDL_MixAudioFormat( ... )
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.
SDL_AudioFormat
SDL_QueueAudio( ... )
Queue more audio on non-callback devices.
If you are looking to retrieve queued audio from a non-callback capture device, you want SDL_DequeueAudio( ... ) instead. SDL_QueueAudio( ... ) will return -1 to signify an error if you use it with capture devices.
SDL_DequeueAudio( ... )
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 function.
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 function copies the supplied data, so you are safe to free it when the function returns. This function 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 function, but not both.
You should not call SDL_LockAudio( ... ) on the device before queueing; SDL handles locking internally for this function.
SDL_LockAudio( ... )
data
Returns 0 on success or a negative error code on failure; call SDL_GetError( ) for more information.
Dequeue more audio on non-callback devices.
If you are looking to queue audio for output on a non-callback playback device, you want SDL_QueueAudio( ... ) instead. SDL_DequeueAudio( ... ) will always return 0 if you use it with playback devices.
SDL offers two ways to retrieve audio from a capture device: you can either supply a callback that SDL triggers with some frequency as the device records more audio data, (push method), or you can supply no callback, and then SDL will expect you to retrieve data at regular intervals (pull method) with this function.
There are no limits on the amount of data you can queue, short of exhaustion of address space. Data from the device will keep queuing as necessary without further intervention from you. This means you will eventually run out of memory if you aren't routinely dequeueing data.
Capture devices will not queue data when paused; if you are expecting to not need captured audio for some length of time, use SDL_PauseAudioDevice() to stop the capture device from queueing more data. This can be useful during, say, level loading times. When unpaused, capture devices will start queueing data from that point, having flushed any capturable data available while paused.
This function is thread-safe, but dequeueing from the same device from two threads at once does not promise which thread will dequeue data first.
You may not dequeue audio from a device that is using an application-supplied callback; doing so returns an error. You have to use the audio callback, or dequeue audio with this function, but not both.
You should not call SDL_LockAudio( ... ) on the device before dequeueing; SDL handles locking internally for this function.
Returns the number of bytes dequeued, which could be less than requested; call SDL_GetError( ) for more information.
SDL_GetQueuedAudioSize( ... )
Get the number of bytes of still-queued audio.
For playback devices: this is the number of bytes that have been queued for playback with SDL_QueueAudio( ... ), but have not yet been sent to the hardware.
Once we've sent it to the hardware, this function 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 function, but it hasn't played any of it yet, or maybe half of it, etc.
For capture devices, this is the number of bytes that have been captured by the device and are waiting for you to dequeue. This number may grow at any time, so this only informs of the lower-bound of available data.
You may not queue or dequeue audio on a device that is using an application-supplied callback; calling this function on such a device always returns 0. You have to use the audio callback or queue audio, but not both.
You should not call SDL_LockAudio( ... ) on the device before querying; SDL handles locking internally for this function.
Returns the number of bytes (not samples!) of queued audio.
SDL_ClearQueuedAudio( ... )
Drop any queued audio data waiting to be sent to the hardware.
Immediately after this call, SDL_GetQueuedAudioSize( ... ) will return 0. For output devices, the hardware will start playing silence if more audio isn't queued. For capture devices, the hardware will start filling the empty queue with new data if the capture device isn't paused.
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 or any unprocessed microphone input during a level change in your game.
You should not call SDL_LockAudio( ... ) on the device before clearing the queue; SDL handles locking internally for this function.
This function always succeeds and thus returns void.
SDL_LockAudio( )
Protects the callback function.
During a SDL_LockAudio( )/SDL_UnlockAudio( ) pair, you can be guaranteed that the callback function is not running. Do not call these from the callback function or you will cause deadlock.
SDL_UnlockAudio( )
SDL_LockAudioDevice( ... )
Protects the callback function for a particular audio device.
During a SDL_LockAudioDevice( ... )/SDL_UnlockAudioDevice( ... ) pair, you can be guaranteed that the callback function is not running. Do not call these from the callback function or you will cause deadlock.
SDL_UnlockAudioDevice( ... )
SDL_CloseAudio( )
This function is a legacy means of closing the audio device.
SDL_CloseAudioDevice( 1 );
and is only useful if you used the legacy SDL_OpenAudio( ... ) function.
SDL_CloseAudioDevice( ... )
This function is a legacy means of closing a particular audio device and is only useful if you used the legacy SDL_OpenAudio( ... ) function.
Defines and enumerations listed here may be imported by name or with their given tags.
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
These may be imported by name or with the :audio tag.
SDL_AUDIO_MASK_BITSIZE
SDL_AUDIO_MASK_DATATYPE
SDL_AUDIO_MASK_ENDIAN
SDL_AUDIO_MASK_SIGNED
SDL_AUDIO_BITSIZE( ... )
SDL_AUDIO_ISFLOAT( ... )
SDL_AUDIO_ISBIGENDIAN( ... )
SDL_AUDIO_ISSIGNED( ... )
SDL_AUDIO_ISINT( ... )
SDL_AUDIO_ISLITTLEENDIAN( ... )
SDL_AUDIO_ISUNSIGNED( ... )
Defaults to LSB byte order. These may be imported with the :audio tag.
AUDIO_U8
AUDIO_S8
AUDIO_U16LSB
AUDIO_S16LSB
AUDIO_U16MSB
AUDIO_S16MSB
AUDIO_U16
AUDIO_S16
int32
These may be imported with the :audio tag.
AUDIO_S32LSB
AUDIO_S32MSB
AUDIO_S32
float32
AUDIO_F32LSB
AUDIO_F32MSB
AUDIO_F32
Values are based on endianness of system. These may be imported with the :audio tag.
AUDIO_U16SYS
AUDIO_S16SYS
AUDIO_S32SYS
AUDIO_F32SYS
Which audio format changes are allowed when opening a device. These may be imported with the :audio tag.
SDL_AUDIO_ALLOW_SAMPLES_CHANGE
SDL_AudioCallback
Callback called when the audio device needs more data.
Parameters you should expect:
userdata
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 SDL_QueueAudio( ) instead, if you like. Just open your audio device with a NULL callback.
SDL_AudioFilter
Callback that feeds the audio device.
SDL_AUDIOCVT_MAX_FILTERS
The maximum number of SDL_AudioFilter functions in SDL2::AudioCVT is currently limited to 9. The SDL2::AudioCVT->filters array has 10 pointers, one of which is the terminating NULL pointer.
SDL Audio Device IDs.
A successful call to SDL_OpenAudio( ... ) is always device id 1, and legacy SDL audio APIs assume you want this device ID. SDL_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.
Get the current audio state. This enumeration may be imported with the :audioStatus tag.
:audioStatus
SDL_AUDIO_STOPPED
SDL_AUDIO_PLAYING
SDL_AUDIO_PAUSED
Max audio volume.
Copyright (C) Sanko Robinson.
This library is free software; you can redistribute it and/or modify it under the terms found in the Artistic License 2. Other copyrights, terms, and conditions may apply to data transmitted through this module.
Sanko Robinson <sanko@cpan.org>
To install SDL2::FFI, copy and paste the appropriate command in to your terminal.
cpanm
cpanm SDL2::FFI
CPAN shell
perl -MCPAN -e shell install SDL2::FFI
For more information on module installation, please visit the detailed CPAN module installation guide.