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

   1 #include "alsa_output.h"
   2
   3 #include <alsa/asoundlib.h>
   4 #include <alsa/error.h>
   5 #include <alsa/pcm.h>
   6 #include <errno.h>
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <vector>
  10
  11 using namespace std;
  12
  13 namespace {
  14
  15 void die_on_error(const char *func_name, int err)
  16 {
  17         if (err < 0) {
  18                 fprintf(stderr, "%s: %s\n", func_name, snd_strerror(err));
  19                 abort();
  20         }
  21 }
  22
  23 }  // namespace
  24
  25 ALSAOutput::ALSAOutput(int sample_rate, int num_channels)
  26         : sample_rate(sample_rate), num_channels(num_channels)
  27 {
  28         die_on_error("snd_pcm_open()", snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, 0));
  29
  30         // Set format.
  31         snd_pcm_hw_params_t *hw_params;
  32         snd_pcm_hw_params_alloca(&hw_params);
  33         die_on_error("snd_pcm_hw_params_any()", snd_pcm_hw_params_any(pcm_handle, hw_params));
  34         die_on_error("snd_pcm_hw_params_set_access()", snd_pcm_hw_params_set_access(pcm_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED));
  35         die_on_error("snd_pcm_hw_params_set_format()", snd_pcm_hw_params_set_format(pcm_handle, hw_params, SND_PCM_FORMAT_FLOAT_LE));
  36         die_on_error("snd_pcm_hw_params_set_rate()", snd_pcm_hw_params_set_rate(pcm_handle, hw_params, sample_rate, 0));
  37         die_on_error("snd_pcm_hw_params_set_channels", snd_pcm_hw_params_set_channels(pcm_handle, hw_params, num_channels));
  38
  39         // Fragment size of 2048 samples. (A frame at 60 fps/48 kHz is 800 samples.)
  40         // We ask for 4 such periods (~170 ms buffer).
  41         unsigned int num_periods = 4;
  42         int dir = 0;
  43         die_on_error("snd_pcm_hw_params_set_periods_near()", snd_pcm_hw_params_set_periods_near(pcm_handle, hw_params, &num_periods, &dir));
  44         period_size = 2048;
  45         dir = 0;
  46         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));
  47         die_on_error("snd_pcm_hw_params()", snd_pcm_hw_params(pcm_handle, hw_params));
  48         //snd_pcm_hw_params_free(hw_params);
  49
  50         snd_pcm_sw_params_t *sw_params;
  51         snd_pcm_sw_params_alloca(&sw_params);
  52         die_on_error("snd_pcm_sw_params_current()", snd_pcm_sw_params_current(pcm_handle, sw_params));
  53         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));
  54         die_on_error("snd_pcm_sw_params()", snd_pcm_sw_params(pcm_handle, sw_params));
  55
  56         die_on_error("snd_pcm_nonblock", snd_pcm_nonblock(pcm_handle, 1));
  57         die_on_error("snd_pcm_prepare()", snd_pcm_prepare(pcm_handle));
  58 }
  59
  60 void ALSAOutput::write(const vector<float> &samples)
  61 {
  62         buffer.insert(buffer.end(), samples.begin(), samples.end());
  63
  64 try_again:
  65         int periods_to_write = buffer.size() / (period_size * num_channels);
  66         if (periods_to_write == 0) {
  67                 return;
  68         }
  69
  70         int ret = snd_pcm_writei(pcm_handle, buffer.data(), periods_to_write * period_size);
  71         if (ret == -EPIPE) {
  72                 fprintf(stderr, "warning: snd_pcm_writei() reported underrun\n");
  73                 snd_pcm_recover(pcm_handle, ret, 1);
  74                 goto try_again;
  75         } else if (ret == -EAGAIN) {
  76                 ret = 0;
  77         } else if (ret < 0) {
  78                 fprintf(stderr, "error: snd_pcm_writei() returned '%s'\n", snd_strerror(ret));
  79                 abort();
  80         } else if (ret > 0) {
  81                 buffer.erase(buffer.begin(), buffer.begin() + ret * num_channels);
  82         }
  83
  84         if (buffer.size() >= period_size * num_channels) {  // Still more to write.
  85                 if (ret == 0) {
  86                         if (buffer.size() >= period_size * num_channels * 8) {
  87                                 // OK, almost 100 ms. Giving up.
  88                                 fprintf(stderr, "warning: ALSA overrun, dropping some audio (%d ms)\n",
  89                                         int(buffer.size() * 1000 / (num_channels * sample_rate)));
  90                                 buffer.clear();
  91                         }
  92                 } else if (ret > 0) {
  93                         // Not a completely failure (effectively a short write),
  94                         // possibly due to a signal.
  95                         goto try_again;
  96                 }
  97         }
  98 }