1 #include "alsa_output.h"
3 #include <alsa/asoundlib.h>
4 #include <alsa/error.h>
15 void die_on_error(const char *func_name, int err)
18 fprintf(stderr, "%s: %s\n", func_name, snd_strerror(err));
25 ALSAOutput::ALSAOutput(int sample_rate, int num_channels)
26 : sample_rate(sample_rate), num_channels(num_channels)
28 die_on_error("snd_pcm_open()", snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, 0));
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));
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;
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));
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);
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));
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));
60 void ALSAOutput::write(const vector<float> &samples)
62 buffer.insert(buffer.end(), samples.begin(), samples.end());
65 int periods_to_write = buffer.size() / (period_size * num_channels);
66 if (periods_to_write == 0) {
70 int ret = snd_pcm_writei(pcm_handle, buffer.data(), periods_to_write * period_size);
72 fprintf(stderr, "warning: snd_pcm_writei() reported underrun\n");
73 snd_pcm_recover(pcm_handle, ret, 1);
75 } else if (ret == -EAGAIN) {
78 fprintf(stderr, "error: snd_pcm_writei() returned '%s'\n", snd_strerror(ret));
81 buffer.erase(buffer.begin(), buffer.begin() + ret * num_channels);
84 if (buffer.size() >= period_size * num_channels) { // Still more to write.
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)));
93 // Not a completely failure (effectively a short write),
94 // possibly due to a signal.