找到我可以使用ALSA播放PCM的所有设备

Question

I use ALSA to play PCM samples. I open the PCM stream with this function:

int snd_pcm_open(snd_pcm_t** pcmp,
        const char* name,
        snd_pcm_stream_t stream,
        int mode);

I'm currently using "default" as the name parameter. I would like to be able to choose other devices. What I cannot understand is how I can determine what are the names of the other available devices.

I attached a USB microphone to my system and aplay and amixer seems to detect the new device. How do I determine the name of that device? Is there any ALSA function to get a list of available devices with their respective names?

Answer 1

I think you can use snd_device_name_hint for enumerating devices. Here is an example. Beware that I haven't compiled it !

char **hints;
/* Enumerate sound devices */
int err = snd_device_name_hint(-1, "pcm", (void***)&hints);
if (err != 0)
   return;//Error! Just return

char** n = hints;
while (*n != NULL) {

    char *name = snd_device_name_get_hint(*n, "NAME");

    if (name != NULL && 0 != strcmp("null", name)) {
        //Copy name to another buffer and then free it
        free(name);
    }
    n++;
}//End of while

//Free hint buffer too
snd_device_name_free_hint((void**)hints);

Answer 2

It was my first requirements to a linux/unix projects where I need to know about all of the available audio devices capability and name. Then I need to use these devices to capture and plaback the audio. What I have done is pretty simple. There is a linux/unix command which is used to find the devices through alsa utility in linux.

It is:

aplay -l

Now what I did is just make a programme to give the out as like as this by alsa.

For everyone's help I have made a (.so) library and a sample Application demonstrating the use of this library in c++.

The output of my library is like-

[root@~]# ./IdeaAudioEngineTest
HDA Intel plughw:0,0
HDA Intel plughw:0,2
USB Audio Device plughw:1,0

This library can also capture and playback the real-time audio data.

It is available with documentation in IdeaAudio library with Duplex Alsa Audio

Answer 3

Just for grins, your program reformatted:

#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <unistd.h>

#include <alsa/asoundlib.h>

void listdev(char *devname)

{

    char** hints;
    int    err;
    char** n;
    char*  name;
    char*  desc;
    char*  ioid;

    /* Enumerate sound devices */
    err = snd_device_name_hint(-1, devname, (void***)&hints);
    if (err != 0) {

        fprintf(stderr, "*** Cannot get device names\n");
        exit(1);

    }

    n = hints;
    while (*n != NULL) {

        name = snd_device_name_get_hint(*n, "NAME");
        desc = snd_device_name_get_hint(*n, "DESC");
        ioid = snd_device_name_get_hint(*n, "IOID");

        printf("Name of device: %s\n", name);
        printf("Description of device: %s\n", desc);
        printf("I/O type of device: %s\n", ioid);
        printf("\n");

        if (name && strcmp("null", name)) free(name);
        if (desc && strcmp("null", desc)) free(desc);
        if (ioid && strcmp("null", ioid)) free(ioid);
        n++;

    }

    //Free hint buffer too
    snd_device_name_free_hint((void**)hints);

}

int main(void)

{

    printf("PCM devices:\n");
    printf("\n");
    listdev("pcm");

    printf("MIDI devices:\n");
    printf("\n");
    listdev("rawmidi");

    return 0;

}