CSC 790 Fall 2009

A good resource for Linux audio programming is provided in the "Open Sound 
System OSS 4.x Programmer's Guide" 

  http://manuals.opensound.com/developer/

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Some #includes you will need

#include <stropts.h>        // for ioctl  
#include <fcntl.h>          // for open and O_WRONLY  
#include <sys/soundcard.h>  // for SNDCTL defines

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The ioctl system calls you will need are given below. Note in most cases
the function returns -1 if an error occurs. You must determine if this
occurs in your program and handle it appropriately.  

Setting the format of the audio samples to DSP signed 16 bit little endian  

    int format = AFMT_S16_LE;
    ioctl(fd_, SNDCTL_DSP_SETFMT, &format);

Setting the format to stereo or mono, returns -1 if error  

    int stereo = 0; // 0 = mono , 1 = stereo  
    ioctl(fd_, SNDCTL_DSP_STEREO, &stereo);

Setting the sampling rate of the device  

    int speed = 8000;
    ioctl(fd_, SNDCTL_DSP_SPEED, &sampleRate);

Finding the amount of buffer space of the device  

   audio_buf_info bi;
   ioctl(fd_, SNDCTL_DSP_GETOSPACE, &bi);
   bufferSize_ = bi.bytes;  

Setting the volume of the device, note range is 0 to 100 (0 is the minimum)   

   int level = (vol)|(vol<<8);  
   ioctl(fd_, SOUND_MIXER_WRITE_VOLUME, &level);  

Finding the amount of empty space in the buffer  

   audio_buf_info bi;  
   ioctl(fd_, SNDCTL_DSP_GETOSPACE, &bi);  
   cout << "number of bytes empty in buffer " << bi.bytes << '\n';