Recording and Playing Back an Audio Stream

The following example shows how to record and play back an audio stream. The UMSBAUDDevice object is derived from the base UMSAudioDevice. The first part of the code records 10 seconds from LINE IN and saves the data in a file called /tmp/audiotest. The second part of the code plays the prerecorded /tmp/audiotest file.

The following example shows that when issuing a query request (get_byte_order) to the UMSAudioDevice, you have to free the string returned. All the query methods allocate strings in the object, and applications are responsible for freeing the string. The example does not test return code; however, real applications should test the return code for early problem detection.

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
 
#include <UMSBAUDDevice.h>
 
void main(argc, argv)
int argc;
char *argv[];
{
 UMSBAUDDevice adev;
 UMSAudioDevice_ReturnCode rc;
 Environment *ev;
 
UMSAudioTypes_Buffer buffer;
 long onesecsize ;
 long read_cnt, transferred_cnt;
 int file;
 long sw;
 long osamples;
 char *obyte_order;
 long lgain;
 long rgain;
 long time;
 long pos;
 int bytespersec ;
 int secondtorecord ;
 long channels ;
 long bits ;
 
/* set up som enviroment */
 
ev = somGetGlobalEnvironment();
adev = UMSBAUDDeviceNew();
 
printf("start record session\n");
 
rc = UMSAudioDevice_open(adev,ev,"/dev/paud0","RECORD", 
          UMSAudioDevice_BlockingIO);
 
/* establish audio attributes */
 channels = 2 ;
 bits  = 16 ;
 
rc = UMSAudioDevice_set_sample_rate(adev,ev,22050,&osamples);
rc = UMSAudioDevice_set_bits_per_sample(adev,ev,bits);
rc = UMSAudioDevice_set_number_of_channels(adev,ev,channels);
rc = UMSAudioDevice_set_audio_format_type(adev,ev,"PCM");
rc = UMSAudioDevice_set_byte_order(adev,ev,"MSB");
rc = UMSAudioDevice_set_number_format(adev,ev,"TWOS COMPLEMENT");
 
rc = UMSAudioDevice_get_byte_order(adev,ev,&obyte_order);
 
/* you have to free the string after the query */
 
if (obyte_order) free(obyte_order);
 
rc = UMSAudioDevice_set_volume(adev,ev,100);
rc = UMSAudioDevice_set_balance(adev,ev,0);
rc = UMSAudioDevice_set_time_format(adev,ev,UMSAudioTypes_Msecs); 
 
 lgain = 100; /*maximum left input gain*/
rgain = 100; /*maimum right input gain*/
rc = UMSAudioDevice_enable_input(adev,ev,"LINE_IN",&lgain,&rgain);
rc = UMSAudioDevice_set_monitor(adev,ev,TRUE);
 
rc = UMSAudioDevice_initialize(adev,ev);
 
secondtorecord = 10 ;
bytespersec = (bits / 8) * channels ;
onesecsize = bytespersec * osamples ;
 
time = 1000 * secondtorecord ;
 
buffer._length = onesecsize ;
buffer._buffer = malloc(onesecsize);
buffer._maximum = onesecsize ;
 
file = open("/tmp/testaudio",O_WRONLY | O_CREAT | O_TRUNC,0644);
rc = UMSAudioDevice_start(adev,ev);
 
/* do the recording */
do
{
rc = UMSAudioDevice_read(adev,ev,&buffer,onesecsize,&sw);
write(file,buffer._buffer, bytespersec * sw);
rc = UMSAudioDevice_get_position(adev,ev,&pos);
}
while(time > pos);
 
rc = UMSAudioDevice_stop(adev,ev);
rc = UMSAudioDevice_close(adev,ev);
close(file);
 
/* playback session */
 
printf("start playback session\n");
 
rc = UMSAudioDevice_open(adev,ev,"/dev/paud0","PLAY",
           UMSAudioDevice_BlockingIO);
 
buffer._length = 0 ;
buffer._maximum = onesecsize ;
 
lgain = 100; /*maximum left input gain*/
rgain = 100; /*maimum right input gain*/
 
rc = UMSAudioDevice_enable_output(adev,ev,"LINE_OUT",&lgain,&rgain);
 
rc = UMSAudioDevice_initialize(adev,ev);
 
file = open("/tmp/testaudio",O_RDONLY,0);
rc = UMSAudioDevice_start(adev,ev);
 
while((transferred_cnt = read(file,buffer._buffer,onesecsize))) 
{
read_cnt = transferred_cnt / bytespersec;
buffer._length = transferred_cnt ;
rc = UMSAudioDevice_write(adev,ev,&buffer,read_cnt,&sw);
}
 
rc = UMSAudioDevice_play_remaining_data(adev,ev,TRUE);
 
UMSAudioDevice_stop(adev,ev);
UMSAudioDevice_close(adev,ev);
 
_somFree(adev);
 
}

For introductory information, see Programming with Audio Device Objects.