Adjust the 'balance' value for the specified volume with the
* specified channel map. v will be modified in place and
* returned. The balance is a value between -1.0f and +1.0f. This
* operation might not be reversible! Also, after this call
* pa_cvolume_get_balance() is not guaranteed to actually return the
* requested balance value (e.g. when the input volume was zero anyway for
* all channels). If no balance value is applicable to
* this channel map the volume will not be modified. See
* pa_channel_map_can_balance(). Will return NULL on error. \since 0.9.15
Adjust the 'balance' value for the specified volume with the * specified channel map. v will be modified in place and * returned. The balance is a value between -1.0f and +1.0f. This * operation might not be reversible! Also, after this call * pa_cvolume_get_balance() is not guaranteed to actually return the * requested balance value (e.g. when the input volume was zero anyway for * all channels). If no balance value is applicable to * this channel map the volume will not be modified. See * pa_channel_map_can_balance(). Will return NULL on error. \since 0.9.15