[pulseaudio-discuss] [PATCH] loopback: underrun_protection argument

[Raman Shyshniou]

This patch adds a underrun_protection argument to
control underrun protection algorithm. Disabling
protection will keep loopback latency regardless
of underruns.
---
 src/modules/module-loopback.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/src/modules/module-loopback.c b/src/modules/module-loopback.c
index aecac0a..c452e1a 100644
--- a/src/modules/module-loopback.c
+++ b/src/modules/module-loopback.c
@@ -45,6 +45,7 @@ PA_MODULE_USAGE(
         "sink=<sink to connect to> "
         "adjust_time=<how often to readjust rates in s> "
         "latency_msec=<latency in ms> "
+        "underrun_protection=<boolean> "
         "format=<sample format> "
         "rate=<sample rate> "
         "channels=<number of channels> "
@@ -90,6 +91,7 @@ struct userdata {
     /* Values from command line configuration */
     pa_usec_t latency;
     pa_usec_t adjust_time;
+    bool underrun_protection;
 
     /* Latency boundaries and current values */
     pa_usec_t min_source_latency;
@@ -158,6 +160,7 @@ static const char* const valid_modargs[] = {
     "sink",
     "adjust_time",
     "latency_msec",
+    "underrun_protection",
     "format",
     "rate",
     "channels",
@@ -325,11 +328,20 @@ static void adjust_rates(struct userdata *u) {
 
     /* If we are seeing underruns then the latency is too small */
     if (u->underrun_counter > 2) {
-        u->underrun_latency_limit = PA_MAX(u->latency, u->minimum_latency) + 5 * PA_USEC_PER_MSEC;
-        u->underrun_latency_limit = PA_CLIP_SUB((int64_t)u->underrun_latency_limit, u->sink_latency_offset + u->source_latency_offset);
-        update_minimum_latency(u, u->sink_input->sink, false);
-        pa_log_warn("Too many underruns, increasing latency to %0.2f ms", (double)u->minimum_latency / PA_USEC_PER_MSEC);
-        u->underrun_counter = 0;
+        int64_t target_latency;
+
+        target_latency = PA_MAX(u->latency, u->minimum_latency);
+
+        if (u->underrun_protection)
+            target_latency += 5 * PA_USEC_PER_MSEC;
+
+        u->underrun_latency_limit = PA_CLIP_SUB(target_latency, u->sink_latency_offset + u->source_latency_offset);
+
+        if (u->minimum_latency < u->underrun_latency_limit) {
+            update_minimum_latency(u, u->sink_input->sink, false);
+            pa_log_warn("Too many underruns, increasing latency to %0.2f ms", (double)u->minimum_latency / PA_USEC_PER_MSEC);
+            u->underrun_counter = 0;
+        }
     }
 
     /* Allow one underrun per hour */
@@ -347,7 +359,7 @@ static void adjust_rates(struct userdata *u) {
     }
     u->adjust_time_stamp = now;
 
-    /* Rates and latencies*/
+    /* Rates and latencies */
     old_rate = u->sink_input->sample_spec.rate;
     base_rate = u->source_output->sample_spec.rate;
 
@@ -1251,6 +1263,7 @@ int pa__init(pa_module *m) {
     pa_source *source = NULL;
     pa_source_output_new_data source_output_data;
     bool source_dont_move;
+    bool underrun_protection = true;
     uint32_t latency_msec;
     pa_sample_spec ss;
     pa_channel_map map;
@@ -1336,10 +1349,16 @@ int pa__init(pa_module *m) {
         goto fail;
     }
 
+    if (pa_modargs_get_value_boolean(ma, "underrun_protection", &underrun_protection) < 0) {
+        pa_log("Failed to parse underrun_protection value.");
+        goto fail;
+    }
+
     m->userdata = u = pa_xnew0(struct userdata, 1);
     u->core = m->core;
     u->module = m;
     u->latency = (pa_usec_t) latency_msec * PA_USEC_PER_MSEC;
+    u->underrun_protection = underrun_protection;
     u->output_thread_info.pop_called = false;
     u->output_thread_info.pop_adjust = false;
     u->output_thread_info.push_called = false;
-- 
1.8.3.1