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

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