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

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

Hi:
    I,ve finished this problem using snd_hctl_ apis. code as below:
 
err = snd_hctl_open(&ctlhandle, "default", 0);elemt = snd_hctl_last_elem(ctlhandle);err = snd_hctl_elem_read(elemt, elemvalue);sndvolume0 = snd_ctl_elem_value_get_integer(elemvalue, 0);sndvolume1 = snd_ctl_elem_value_get_integer(elemvalue, 1);
//Modified the sndvolume as we want.
snd_ctl_elem_value_set_integer(elemvalue, 0, sndvolume0);snd_ctl_elem_value_set_integer(elemvalue, 1, sndvolume1);snd_hctl_elem_write(elemt, elemvalue);snd_hctl_wait(ctlhandle, 100);
that code works, but the effect must be in this situations:
 use snd_hctl_open() after snd_pcm_open();  
other the set_value won't work. i don't know why, but i can use this for my code.
 
and that's over of this question.




From: blu...@ho...To: als...@li...Date: Sun, 31 Aug 2008 22:10:52 +0800Subject: [Alsa-user] how can i use alsa-lib api to control pcm playback volume.

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.
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