I Found it out.. hope it helps someone.
snd_pcm_t *capture_handle; snd_pcm_hw_params_t *hw_params;
snd_pcm_open( &capture_handle, str, SND_PCM_STREAM_PLAYBACK, 0 ); snd_pcm_hw_params_malloc (&hw_params);
snd_pcm_hw_params_any(capture_handle, hw_params);
unsigned int num_canais = 0; int ret;
ret = snd_pcm_hw_params_get_channels(hw_params, &num_canais);
printf("Number of channels: %i\n",num_canais);
2011/6/8 André Prado andreprado88@gmail.com:
Hello. I am new to Alsa programming and i want to get the number of input channels on an audio device. I am reading a lot of tutorials and documentations but i am struggling to do this.
Here is a code i've saw to Lists the hardware names of MIDI output device/sub-devices. I've understood it. But i want to get the number of input channels.
Any help is appreciated. THanks
// listmidi.c // Lists the hardware names of MIDI output device/sub-devices // upon each ALSA sound card in the system. // // Compile as: // gcc -o listmidi listmidi.c -lasound
#include <stdio.h> #include <string.h> #include <alsa/asoundlib.h>
int main(int argc, char **argv) { register int err; int cardNum;
// Start with first card cardNum = -1;
for (;;) { snd_ctl_t *cardHandle;
// Get next sound card's card number. When "cardNum" == -1, then ALSA // fetches the first card if ((err = snd_card_next(&cardNum)) < 0) { printf("Can't get the next card number: %s\n", snd_strerror(err)); break; }
// No more cards? ALSA sets "cardNum" to -1 if so if (cardNum < 0) break;
// Open this card's control interface. We specify only the card number -- not // any device nor sub-device too { char str[64];
sprintf(str, "hw:%i", cardNum); if ((err = snd_ctl_open(&cardHandle, str, 0)) < 0) { printf("Can't open card %i: %s\n", cardNum, snd_strerror(err)); continue; } }
{ int devNum;
// Start with the first MIDI device on this card devNum = -1;
for (;;) { snd_rawmidi_info_t *rawMidiInfo; register int subDevCount, i;
// Get the number of the next MIDI device on this card if ((err = snd_ctl_rawmidi_next_device(cardHandle, &devNum)) < 0) { printf("Can't get next MIDI device number: %s\n", snd_strerror(err)); break; }
// No more MIDI devices on this card? ALSA sets "devNum" to -1 if so. // NOTE: It's possible that this sound card may have no MIDI devices on it // at all, for example if it's only a digital audio card if (devNum < 0) break;
// To get some info about the subdevices of this MIDI device (on the card), we need a // snd_rawmidi_info_t, so let's allocate one on the stack snd_rawmidi_info_alloca(&rawMidiInfo); memset(rawMidiInfo, 0, snd_rawmidi_info_sizeof());
// Tell ALSA which device (number) we want info about snd_rawmidi_info_set_device(rawMidiInfo, devNum);
// Get info on the MIDI outs of this device snd_rawmidi_info_set_stream(rawMidiInfo, SND_RAWMIDI_STREAM_OUTPUT);
i = -1; subDevCount = 1;
// More subdevices? while (++i < subDevCount) { // Tell ALSA to fill in our snd_rawmidi_info_t with info on this subdevice snd_rawmidi_info_set_subdevice(rawMidiInfo, i); if ((err = snd_ctl_rawmidi_info(cardHandle, rawMidiInfo)) < 0) { printf("Can't get info for MIDI output subdevice hw:%i,%i,%i: %s\n", cardNum, devNum, i, snd_strerror(err)); continue; }
// Print out how many subdevices (once only) if (!i) { subDevCount = snd_rawmidi_info_get_subdevices_count(rawMidiInfo); printf("\nFound %i MIDI output subdevices on card %i\n", subDevCount, cardNum); }
// NOTE: If there's only one subdevice, then the subdevice number is immaterial, // and can be omitted when you specify the hardware name printf((subDevCount > 1 ? " hw:%i,%i,%i\n" : " hw:%i,%i\n"), cardNum, devNum, i); } } }
// Close the card's control interface after we're done with it snd_ctl_close(cardHandle); }
snd_config_update_free_global(); }
-- Att André