SDL::Audio -- SDL Bindings for Audio

TODO, Core, Audio

Opens the audio device with the desired parameters.

  use SDL;
  use SDL::Audio;

  SDL::init(SDL_INIT_AUDIO);

  my $desired = SDL::AudioSpec->new();

  my $obtained;

  SDL::open_audio($desired, $obtained);

  # $obtained->... (A new SDL::AudioSpec now);

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 hardware audio format if necessary. This function returns -1 if it failed to open the audio device, or couldn't set up the audio thread.

To open the audio device a desired SDL::AudioSpec must be created.

  my $desired = SDL::AudioSpec->new();

You must then fill this structure with your desired audio specifications.

The desired audio frequency in samples-per-second.

    $desired->freq

The desired audio format. See SDL::AudioSpec

    $desired->format

The desired channels (1 for mono, 2 for stereo, 4 for surround, 6 for surround with center and lfe).

    $desired->channels

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 8192 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->samples

This should be set to a function 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 function usually runs in a separate thread, and so you should protect data structures that it accesses by calling SDL::Audio::lock and SDL::Audio::unlock in your code.

THIS IS NOT READY YET

    $desired->callback

    my $callback= sub{ my ($userdata, $stream, $len) = @_;  };

    $userdata is a reference stored in the userdata field of the SDL::AudioSpec. 
    $stream is a pointer to the audio buffer you want to fill with information and $len is the length of the audio buffer in bytes.

    $desired->userdata

    This pointer is passed as the first parameter to the callback function. 

SDL::Audio::open reads these fields from the desired SDL::AudioSpec structure passed to the function and attempts to find an audio configuration matching your desired. As mentioned above, if the obtained parameter is NULL then SDL with convert from your desired audio settings to the hardware settings as it plays.

If obtained is NULL then the desired SDL::AudioSpec is your working specification, otherwise the obtained SDL::AudioSpec becomes the working specification and the desired specification can be deleted. The data in the working specification is used when building SDL::AudioCVT's for converting loaded data to the hardware format.

SDL::Audio::open calculates the size and silence fields for both the $desired and $obtained specifications. The size field stores the total size of the audio buffer in bytes, while the silence stores the value used to represent silence in the audio buffer

The audio device starts out playing silence when it's opened, and should be enabled for playing by calling SDL::Audio::pause(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.

Pauses and unpauses the audio callback processing

Gets the current audio state

Loads a WAVE file

Frees previously opened WAV data

 SDL::Audio->convert( cvt, data, len )

Converts audio data to a desired audio format.

convert_audio takes as first parameter cvt, which was previously initialized. Initializing a SDL::AudioCVT is a two step process. First of all, the structure must be created via SDL::AudioCVT-build> along with source and destination format parameters. Secondly, the data and len fields must be setup. data should point to the audio data buffer beeing source and destination at once and len should be set to the buffer length in bytes. Remember, the length of the buffer pointed to by buf should be len*len_mult bytes in length.

Once the SDL::AudioCVT structure is initialized, we can pass it to convert_audio, which will convert the audio data pointed to by data. If convert_audio fails undef is returned, otherwise the converted SDL::AudioCVT structure.

If the conversion completed successfully then the converted audio data can be read from cvt-buf>. The amount of valid, converted, audio data in the buffer is equal to cvt-len*cvt->len_ratio>.

Example:

 use SDL;
 use SDL::Audio;
 use SDL::AudioSpec;
 use SDL::AudioCVT;

 SDL::init(SDL_INIT_AUDIO);

 # Converting some WAV data to hardware format

 my $desired  = SDL::AudioSpec->new();
 my $obtained = SDL::AudioSpec->new();

 # Set desired format
 $desired->freq(22050);
 $desired->channels(1);
 $desired->format(AUDIO_S16);
 $desired->samples(8192);

 # Open the audio device
 if( SDL::Audio::open($desired, $obtained) < 0 )
 {
     printf( STDERR "Couldn't open audio: %s\n", SDL::get_error() );
     exit(-1);
 }

 # Load the test.wav
 my $wav_ref = SDL::Audio::load_wav('../../test/data/sample.wav', $obtained);

 unless( $wav_ref )
 {
     warn("Could not open sample.wav: %s\n", SDL::get_error() );
     SDL::Audio::close_audio();
     SDL::quit;
     exit(-1);
 }

 my ( $wav_spec, $wav_buf, $wav_len ) = @{$wav_ref};

 # Build AudioCVT
 my $wav_cvt = SDL::AudioCVT->build( $wav_spec->format, $wav_spec->channels, $wav_spec->freq,
                                     $obtained->format, $obtained->channels, $obtained->freq); 

 # Check that the convert was built
 if( $wav_cvt == -1 )
 {
     warn("Couldn't build converter!\n" );
     SDL::Audio::close();
     SDL::Audio::free_wav($wav_buf);
     SDL::quit();
     exit(-1);
 }

 # And now we're ready to convert
 SDL::Audio::convert($wav_cvt, $wav_buf, $wav_len);




 # We can freeto original WAV data now
 SDL::Audio::free_wav($wav_buf);

 


 

TODO: What to do with it? How to use callback? See http://www.libsdl.org/cgi/docwiki.cgi/SDL_ConvertAudio

Mixes audio data

Locks out the callback function

Unlocks the callback function

Shuts down audio processing and closes the audio device.