Do some ALSA tweaks that will hopefully get rid of the underrun loops.

diff --git a/alsa_output.cpp b/alsa_output.cpp
index 52f4936924f7a84570b92aa168af9a79321a735d..a3d17a2088ca0a49ad9ababfa118363150a07147 100644 (file)
--- a/alsa_output.cpp
+++ b/alsa_output.cpp
@@ -31,17 +31,24 @@ ALSAOutput::ALSAOutput(int sample_rate, int num_channels)
        die_on_error("snd_pcm_hw_params_set_channels", snd_pcm_hw_params_set_channels(pcm_handle, hw_params, num_channels));
 
        // Fragment size of 512 samples. (A frame at 60 fps/48 kHz is 800 samples.)
-       // We ask for four such periods.
-       unsigned int num_periods = 4;
+       // We ask for 16 such periods (~170 ms buffer).
+       unsigned int num_periods = 16;
        int dir = 0;
-       die_on_error("snd_pcm_hw_params_set_periods_near", snd_pcm_hw_params_set_periods_near(pcm_handle, hw_params, &num_periods, &dir));
+       die_on_error("snd_pcm_hw_params_set_periods_near()", snd_pcm_hw_params_set_periods_near(pcm_handle, hw_params, &num_periods, &dir));
        period_size = 512;
        dir = 0;
-       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));
-       die_on_error("snd_pcm_hw_params", snd_pcm_hw_params(pcm_handle, hw_params));
+       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));
+       die_on_error("snd_pcm_hw_params()", snd_pcm_hw_params(pcm_handle, hw_params));
        //snd_pcm_hw_params_free(hw_params);
 
+       snd_pcm_sw_params_t *sw_params;
+       snd_pcm_sw_params_alloca(&sw_params);
+       die_on_error("snd_pcm_sw_params_current()", snd_pcm_sw_params_current(pcm_handle, sw_params));
+       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));
+       die_on_error("snd_pcm_sw_params()", snd_pcm_sw_params(pcm_handle, sw_params));
+
        die_on_error("snd_pcm_nonblock", snd_pcm_nonblock(pcm_handle, 1));
+       die_on_error("snd_pcm_prepare()", snd_pcm_prepare(pcm_handle));
 }
 
 void ALSAOutput::write(const vector<float> &samples)