also I found next explanation:
/**
* Call settings.
*/
typedef struct pjsua_call_setting
{
///...
/**
* Number of simultaneous active audio streams for this call. Setting
* this to zero will disable audio in this call.
*
* Default: 1
*/
unsigned aud_cnt;
///...
} pjsua_call_setting;
looks like it what you need!
