Update alsa backend.

src/cubeb_alsa.c

@@ -774,7 +774,7 @@ alsa_stream_init(cubeb * ctx, cubeb_stream ** stream, char const * stream_name,
                  cubeb_stream_params * input_stream_params,
                  cubeb_devid output_device,
                  cubeb_stream_params * output_stream_params,
-                 unsigned int latency,
+                 unsigned int latency_frames,
                  cubeb_data_callback data_callback, cubeb_state_callback state_callback,
                  void * user_ptr)
 {
@@ -782,6 +782,8 @@ alsa_stream_init(cubeb * ctx, cubeb_stream ** stream, char const * stream_name,
   int r;
   snd_pcm_format_t format;
   snd_pcm_uframes_t period_size;
+  int latency_us = 0;
+
 
   assert(ctx && stream);
 
@@ -845,16 +847,19 @@ alsa_stream_init(cubeb * ctx, cubeb_stream ** stream, char const * stream_name,
   r = snd_pcm_nonblock(stm->pcm, 1);
   assert(r == 0);
 
+  latency_us = latency_frames * 1e6 / stm->params.rate;
+
   /* Ugly hack: the PA ALSA plugin allows buffer configurations that can't
      possibly work.  See https://bugzilla.mozilla.org/show_bug.cgi?id=761274.
      Only resort to this hack if the handle_underrun workaround failed. */
   if (!ctx->local_config && ctx->is_pa) {
-    latency = latency < 500 ? 500 : latency;
+    const int min_latency = 5e5;
+    latency_us = latency_us < min_latency ? min_latency: latency_us;
   }
 
   r = snd_pcm_set_params(stm->pcm, format, SND_PCM_ACCESS_RW_INTERLEAVED,
                          stm->params.channels, stm->params.rate, 1,
-                         latency * 1000);
+                         latency_us);
   if (r < 0) {
     alsa_stream_destroy(stm);
     return CUBEB_ERROR_INVALID_FORMAT;
@@ -999,11 +1004,11 @@ alsa_get_preferred_sample_rate(cubeb * ctx, uint32_t * rate) {
 }
 
 static int
-alsa_get_min_latency(cubeb * ctx, cubeb_stream_params params, uint32_t * latency_ms)
+alsa_get_min_latency(cubeb * ctx, cubeb_stream_params params, uint32_t * latency_frames)
 {
-  /* This is found to be an acceptable minimum, even on a super low-end
+  /* 40ms is found to be an acceptable minimum, even on a super low-end
    * machine. */
-  *latency_ms = 40;
+  *latency_frames = 40 * params.rate / 1000;
 
   return CUBEB_OK;
 }