git.sesse.net Git - nageru/blob - alsa_output.cpp

   1 #include "alsa_output.h"
   2
   3 #include <alsa/asoundlib.h>
   4 #include <errno.h>
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <vector>
   8
   9 using namespace std;
  10
  11 namespace {
  12
  13 void die_on_error(const char *func_name, int err)
  14 {
  15         if (err < 0) {
  16                 fprintf(stderr, "%s: %s\n", func_name, snd_strerror(err));
  17                 exit(1);
  18         }
  19 }
  20
  21 }  // namespace
  22
  23 ALSAOutput::ALSAOutput(int sample_rate, int num_channels)
  24         : sample_rate(sample_rate), num_channels(num_channels)
  25 {
  26         die_on_error("snd_pcm_open()", snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, 0));
  27
  28         // Set format.
  29         snd_pcm_hw_params_t *hw_params;
  30         snd_pcm_hw_params_alloca(&hw_params);
  31         die_on_error("snd_pcm_hw_params_any()", snd_pcm_hw_params_any(pcm_handle, hw_params));
  32         die_on_error("snd_pcm_hw_params_set_access()", snd_pcm_hw_params_set_access(pcm_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED));
  33         die_on_error("snd_pcm_hw_params_set_format()", snd_pcm_hw_params_set_format(pcm_handle, hw_params, SND_PCM_FORMAT_FLOAT_LE));
  34         die_on_error("snd_pcm_hw_params_set_rate()", snd_pcm_hw_params_set_rate(pcm_handle, hw_params, sample_rate, 0));
  35         die_on_error("snd_pcm_hw_params_set_channels", snd_pcm_hw_params_set_channels(pcm_handle, hw_params, num_channels));
  36
  37         // Fragment size of 512 samples. (A frame at 60 fps/48 kHz is 800 samples.)
  38         // We ask for 16 such periods (~170 ms buffer).
  39         unsigned int num_periods = 16;
  40         int dir = 0;
  41         die_on_error("snd_pcm_hw_params_set_periods_near()", snd_pcm_hw_params_set_periods_near(pcm_handle, hw_params, &num_periods, &dir));
  42         period_size = 512;
  43         dir = 0;
  44         die_on_error("snd_pcm_hw_params_set_period_size_near()", snd_pcm_hw_params_set_period_size_near(pcm_handle, hw_params, &period_size, &dir));
  45         die_on_error("snd_pcm_hw_params()", snd_pcm_hw_params(pcm_handle, hw_params));
  46         //snd_pcm_hw_params_free(hw_params);
  47
  48         snd_pcm_sw_params_t *sw_params;
  49         snd_pcm_sw_params_alloca(&sw_params);
  50         die_on_error("snd_pcm_sw_params_current()", snd_pcm_sw_params_current(pcm_handle, sw_params));
  51         die_on_error("snd_pcm_sw_params_set_start_threshold", snd_pcm_sw_params_set_start_threshold(pcm_handle, sw_params, num_periods * period_size / 2));
  52         die_on_error("snd_pcm_sw_params()", snd_pcm_sw_params(pcm_handle, sw_params));
  53
  54         die_on_error("snd_pcm_nonblock", snd_pcm_nonblock(pcm_handle, 1));
  55         die_on_error("snd_pcm_prepare()", snd_pcm_prepare(pcm_handle));
  56 }
  57
  58 void ALSAOutput::write(const vector<float> &samples)
  59 {
  60         buffer.insert(buffer.end(), samples.begin(), samples.end());
  61
  62 try_again:
  63         int periods_to_write = buffer.size() / (period_size * num_channels);
  64         if (periods_to_write == 0) {
  65                 return;
  66         }
  67
  68         int ret = snd_pcm_writei(pcm_handle, buffer.data(), periods_to_write * period_size);
  69         if (ret == -EPIPE) {
  70                 fprintf(stderr, "warning: snd_pcm_writei() reported underrun\n");
  71                 snd_pcm_recover(pcm_handle, ret, 1);
  72                 goto try_again;
  73         } else if (ret == -EAGAIN) {
  74                 ret = 0;
  75         } else if (ret < 0) {
  76                 fprintf(stderr, "error: snd_pcm_writei() returned '%s'\n", snd_strerror(ret));
  77                 exit(1);
  78         } else if (ret > 0) {
  79                 buffer.erase(buffer.begin(), buffer.begin() + ret * num_channels);
  80         }
  81
  82         if (buffer.size() >= period_size * num_channels) {  // Still more to write.
  83                 if (ret == 0) {
  84                         if (buffer.size() >= period_size * num_channels * 8) {
  85                                 // OK, almost 100 ms. Giving up.
  86                                 fprintf(stderr, "warning: ALSA overrun, dropping some audio (%d ms)\n",
  87                                         int(buffer.size() * 1000 / (num_channels * sample_rate)));
  88                                 buffer.clear();
  89                         }
  90                 } else if (ret > 0) {
  91                         // Not a completely failure (effectively a short write),
  92                         // possibly due to a signal.
  93                         goto try_again;
  94                 }
  95         }
  96 }