RAOP: Announce real latency

Use predefined values depending on the server, and make it configurable.
AirPlay is supposed to have 2s of latency. With my hardware, this is
more 2.352 seconds after numerous tests.
Switch from pausing/resuming the smoother to resetting it because the
smoother got stuck returning the same value after an idle/running cycle,
making latency calculation wrong.

src/modules/raop/module-raop-discover.c

@@ -44,11 +44,14 @@
 #include <pulsecore/avahi-wrap.h>
 
 #include "module-raop-discover-symdef.h"
+#include "raop-util.h"
 
 PA_MODULE_AUTHOR("Colin Guthrie");
 PA_MODULE_DESCRIPTION("mDNS/DNS-SD Service Discovery of RAOP devices");
 PA_MODULE_VERSION(PACKAGE_VERSION);
 PA_MODULE_LOAD_ONCE(true);
+PA_MODULE_USAGE(
+        "latency_msec=<audio latency - applies to all devices> ");
 
 #define SERVICE_TYPE_SINK "_raop._tcp"
 
@@ -61,9 +64,13 @@ struct userdata {
     AvahiServiceBrowser *sink_browser;
 
     pa_hashmap *tunnels;
+
+    bool latency_set;
+    uint32_t latency;
 };
 
 static const char* const valid_modargs[] = {
+    "latency_msec",
     NULL
 };
 
@@ -127,6 +134,23 @@ static void tunnel_free(struct tunnel *t) {
     pa_xfree(t);
 }
 
+/* This functions returns RAOP audio latency as guessed by the
+ * device model header.
+ * Feel free to complete the possible values after testing with
+ * your hardware.
+ */
+static uint32_t guess_latency_from_device(const char *model) {
+    uint32_t default_latency = RAOP_DEFAULT_LATENCY;
+
+    if (pa_streq(model, "PIONEER,1")) {
+        /* Pioneer N-30 */
+        default_latency = 2352;
+    }
+
+    pa_log_debug("Default latency is %u ms for device model %s.", default_latency, model);
+    return default_latency;
+}
+
 static void resolver_cb(
         AvahiServiceResolver *r,
         AvahiIfIndex interface, AvahiProtocol protocol,
@@ -145,6 +169,7 @@ static void resolver_cb(
     char at[AVAHI_ADDRESS_STR_MAX];
     AvahiStringList *l;
     pa_module *m;
+    uint32_t latency = RAOP_DEFAULT_LATENCY;
 
     pa_assert(u);
 
@@ -226,6 +251,9 @@ static void resolver_cb(
             /* Sample rate */
             pa_xfree(sr);
             sr = pa_xstrdup(value);
+        } else if (pa_streq(key, "am")) {
+            /* Device model */
+            latency = guess_latency_from_device(value);
         }
 
         avahi_free(key);
@@ -308,6 +336,13 @@ static void resolver_cb(
         pa_xfree(t);
     }
 
+    if (u->latency_set)
+        latency = u->latency;
+
+    t = args;
+    args = pa_sprintf_malloc("%s latency_msec=%u", args, latency);
+    pa_xfree(t);
+
     pa_log_debug("Loading module-raop-sink with arguments '%s'", args);
 
     if (pa_module_load(&m, u->core, "module-raop-sink", args) >= 0) {
@@ -432,10 +467,17 @@ int pa__init(pa_module *m) {
         goto fail;
     }
 
-    m->userdata = u = pa_xnew(struct userdata, 1);
+    m->userdata = u = pa_xnew0(struct userdata, 1);
     u->core = m->core;
     u->module = m;
-    u->sink_browser = NULL;
+
+    if (pa_modargs_get_value(ma, "latency_msec", NULL) != NULL) {
+        u->latency_set = true;
+        if (pa_modargs_get_value_u32(ma, "latency_msec", &u->latency) < 0) {
+            pa_log("Failed to parse latency_msec argument.");
+            goto fail;
+        }
+    }
 
     u->tunnels = pa_hashmap_new(tunnel_hash, tunnel_compare);