pulse-server: add a pulse.zeroramp.gap property

Add a new pulse.zeroramp.gap property that will enable gap detection and
fade-in/fade-out on gaps on playback streams.

Make a rule to enable this on chrome, which does not do a cork/pause
when a stream is paused but sends out silence. With the gap detection
enabled, this allows the audioconvert to perform fades to avoid pops and
clocks from sudden DC changes at the gaps.

Fixes #4745

src/daemon/pipewire-pulse.conf.in

@@ -142,6 +142,7 @@ pulse.properties = {
     #pulse.max-sample-cache = 67108864      # max total sample cache size (64MB)
     #pulse.default.format   = F32
     #pulse.default.position = [ FL FR ]
+    #pulse.zeroramp.gap     = 0             # detect silence of N samples and fade-in/out
 }
 
 pulse.properties.rules = [
@@ -209,4 +210,13 @@ pulse.rules = [
     #    matches = [ { application.process.binary = "Discord" } ]
     #    actions = { quirks = [ block-source-volume ] }
     #}
+
+    {
+        matches = [ { application.process.binary = "chrome" } ]
+        actions = {
+            update-props = {
+                pulse.zeroramp.gap     = 8
+            }
+        }
+    }
 ]

src/modules/module-protocol-pulse.c

@@ -77,7 +77,8 @@
  *     #pulse.default.position = [ FL FR ]
  *     #pulse.idle.timeout     = 0
  *     #pulse.max-streams      = 64
- *     #pulse.max-sample-cache   = 67108864
+ *     #pulse.max-sample-cache = 67108864
+ *     #pulse.zeroramp.gap     = 0             # detect silence of N samples and fade-in/out
  * }
  *
  * pulse.properties.rules = [
@@ -262,6 +263,14 @@
  * The maximum total size in bytes of all sample cache entries. Default is
  * 67108864 (64MB).
  *
+ *\code{.unparsed}
+ *     pulse.zeroramp.gap = 0
+ *\endcode
+ *
+ * Enable silence detection of a playback stream and perform fade-in and fade-out on
+ * silence boundaries to avoid loud pops. This is a workaround for when the application
+ * sends silence instead of corking/uncorking to pause/resume the stream.
+ *
  * ## Command execution
  *
  * As part of the server startup sequence, a set of commands can be executed.

src/modules/module-protocol-pulse/internal.h

@@ -38,6 +38,7 @@ struct defs {
 	uint32_t idle_timeout;
 	uint32_t max_streams;
 	uint32_t max_sample_cache;
+	uint32_t zeroramp_gap;
 };
 
 struct stats {

src/modules/module-protocol-pulse/pulse-server.c

@@ -69,6 +69,7 @@
 #define DEFAULT_IDLE_TIMEOUT		"0"
 #define DEFAULT_MAX_STREAMS		"64"
 #define DEFAULT_MAX_SAMPLE_CACHE	"67108864"
+#define DEFAULT_ZERORAMP_GAP		"0"
 
 #define MAX_FORMATS	32
 /* The max amount of data we send in one block when capturing. In PulseAudio this
@@ -1837,6 +1838,9 @@ static int do_create_playback_stream(struct client *client, uint32_t command, ui
 	if (dont_inhibit_auto_suspend)
 		pw_properties_set(props, PW_KEY_NODE_PASSIVE, "true");
 
+	if (impl->defs.zeroramp_gap > 0)
+		pw_properties_setf(props, "zeroramp.gap", "%d", impl->defs.zeroramp_gap);
+
 	stream->stream = pw_stream_new(client->core, name, spa_steal_ptr(props));
 	if (stream->stream == NULL)
 		goto error_errno;
@@ -5666,6 +5670,7 @@ static void load_defaults(struct defs *def, struct pw_properties *props)
 	parse_uint32(props, "pulse.idle.timeout", DEFAULT_IDLE_TIMEOUT, &def->idle_timeout);
 	parse_uint32(props, "pulse.max-streams", DEFAULT_MAX_STREAMS, &def->max_streams);
 	parse_uint32(props, "pulse.max-sample-cache", DEFAULT_MAX_SAMPLE_CACHE, &def->max_sample_cache);
+	parse_uint32(props, "pulse.zeroramp.gap", DEFAULT_ZERORAMP_GAP, &def->zeroramp_gap);
 	def->sample_spec.channels = def->channel_map.channels;
 	def->quantum_limit = 8192;
 }