a2dp: automatic delay estimation

spa/plugins/bluez5/a2dp-sink.c

@@ -616,9 +616,11 @@ static void a2dp_on_timeout(struct spa_source *source)
 		this->clock->nsec = now_time;
 		this->clock->position += duration;
 		this->clock->duration = duration;
-		this->clock->delay = 0;
 		this->clock->rate_diff = 1.0f;
 		this->clock->next_nsec = this->next_time;
+
+		// The bluetooth AVDTP delay value is measured in units of 100us
+		this->clock->delay = (100 * this->transport->delay * (int64_t) this->clock->rate.denom) / SPA_USEC_PER_SEC;
 	}
 
 	spa_log_debug(this->log, NAME" %p: timeout %"PRIu64" %"PRIu64"", this,

spa/plugins/bluez5/bluez5-dbus.c

@@ -814,6 +814,17 @@ static int transport_update_props(struct spa_bt_transport *transport,
 		}
 		else if (strcmp(key, "Volume") == 0) {
 		}
+		else if (strcmp(key, "Delay") == 0) {
+			uint16_t value;
+
+			if (type != DBUS_TYPE_UINT16)
+				goto next;
+			dbus_message_iter_get_basic(&it[1], &value);
+
+			spa_log_debug(monitor->log, "transport %p: %s=%02x", transport, key, value);
+
+			transport->delay = value;
+		}
 	      next:
 		dbus_message_iter_next(props_iter);
 	}

spa/plugins/bluez5/defs.h

@@ -288,6 +288,7 @@ struct spa_bt_transport {
 	int fd;
 	uint16_t read_mtu;
 	uint16_t write_mtu;
+	uint16_t delay;
 	void *user_data;
 
 	struct spa_hook_list listener_list;