Hi all,
I've got a simple PCM capture test program below, which is basically a slightly tweak version of something from:
http://equalarea.com/paul/alsa-audio.html
The program uses two different methods of setting up the capture handle; one that works (and is complex) and one that doesn't but seems like it should (and is simple). I'm trying to figure out why the simple one (using snd_pcm_set_params) doesn't work.
The program can be compiled and run in two ways:
gcc -Wall -O2 -DUSE_SET_PARAMS=1 alsa_capture.c -lasound -o alsa_capture ./alsa_capture
which fails with:
Read from audio interface failed (Input/output error)
and:
gcc -Wall -O2 -DUSE_SET_PARAMS=0 alsa_capture.c -lasound -o alsa_capture ./alsa_capture
which works as expected.
Questions:
* Is snd_pcm_set_params() supposed to work on capture handles (I've used it successfully on playback handles)?
* Is my use of snd_pcm_set_params() missing something and if so what?
* If snd_pcm_set_params() is not supposed to work on capture handles would it be possible to update the documentation to reflect that?
Thanks, Erik
//--------------------------------------------- #include <stdio.h> #include <stdlib.h>
#include <alsa/asoundlib.h> #include <alsa/pcm.h>
int main (int argc, char *argv[]) { int i; int err; char *buffer; int buffer_frames = 128; unsigned int rate = 44100; snd_pcm_t *capture_handle; snd_pcm_format_t format = SND_PCM_FORMAT_S32_LE;
char* device = "default"; if (argc > 1) device = argv[1];
if ((err = snd_pcm_open (&capture_handle, device, SND_PCM_STREAM_CAPTURE, 0)) < 0) { printf ("Cannot open audio device %s (%s)\n", device, snd_strerror (err)); exit (1) ; }
if (USE_SET_PARAMS) { if ((err = snd_pcm_set_params (capture_handle, format, SND_PCM_ACCESS_RW_INTERLEAVED, 2, rate, 0, 500000)) < 0) { /* 0.5sec */ printf ("Capture open error: %s\n", snd_strerror (err)); exit (1) ; } } else { snd_pcm_hw_params_t *hw_params;
if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) { printf ("Cannot allocate hardware parameter structure (%s)\n", snd_strerror (err)); exit (1) ; }
if ((err = snd_pcm_hw_params_any (capture_handle, hw_params)) < 0) { printf ("Cannot initialize hardware parameter structure (%s)\n", snd_strerror (err)); exit (1) ; }
if ((err = snd_pcm_hw_params_set_access (capture_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) { printf ("cannot set access type (%s)\n", snd_strerror (err)); exit (1) ; }
if ((err = snd_pcm_hw_params_set_format (capture_handle, hw_params, format)) < 0) { printf ("Cannot set sample format (%s)\n", snd_strerror (err)); exit (1) ; }
if ((err = snd_pcm_hw_params_set_rate_near (capture_handle, hw_params, &rate, 0)) < 0) { printf ("Cannot set sample rate (%s)\n", snd_strerror (err)); exit (1) ; }
if ((err = snd_pcm_hw_params_set_channels (capture_handle, hw_params, 2)) < 0) { printf ("cannot set channel count (%s)\n", snd_strerror (err)); exit (1) ; }
if ((err = snd_pcm_hw_params (capture_handle, hw_params)) < 0) { printf ("cannot set parameters (%s)\n", snd_strerror (err)); exit (1) ; }
snd_pcm_hw_params_free (hw_params); }
buffer = malloc (buffer_frames * snd_pcm_format_width(format) / 8 * 2);
if ((err = snd_pcm_prepare (capture_handle)) < 0) { printf ("cannot prepare audio interface for use (%s)\n", snd_strerror (err)); exit (1) ; }
for (i = 0; i < 10; ++i) { if ((err = snd_pcm_readi (capture_handle, buffer, buffer_frames)) != buffer_frames) { printf ("Read from audio interface failed (%s)\n", snd_strerror (err)); exit (1) ; break; } printf("read %d done\n", i); }
free(buffer);
snd_pcm_close (capture_handle); puts ("Audio interface closed");
return 0; }