[Alsa-user] how can i use alsa-lib api to control pcm playback volume.

[Falcon.Xu <blu...@ho...>]

Hi:
    i'm doing some develop on a linux system, kernel version: 2.6.23.9.   alsa-lib version:1.0.15.
now ffmpeg and alsa can work together to playback mp3/aac file. during this step:

snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
set_params(); //set hw and sw params.
while(audio_data)
{
decode_audio_data(&audio_data, &data_len);
snd_pcm_writei(audio_data. data_len);
} 

and the mp3 playback is ok, now i'm going to add the volume control functions when the sound is playback.
but when i read the alsa-lib api funtions reference, i can not clearly know how i can control the pcm volume by alsa-lib functions.
and in alsamixer and amixer functions, seems complex to complete the operation. is it has a simple way to control the pcm volume?  thanks for any suggestions.