diff --git a/spa/plugins/control/mixer.c b/spa/plugins/control/mixer.c
index 9085da5c5..c19d82ebc 100644
--- a/spa/plugins/control/mixer.c
+++ b/spa/plugins/control/mixer.c
@@ -39,6 +39,8 @@ struct buffer {
 };
 
 struct port {
+	struct spa_list link;
+
 	uint32_t direction;
 	uint32_t id;
 
@@ -48,7 +50,6 @@ struct port {
 	struct spa_port_info info;
 	struct spa_param_info params[8];
 
-	unsigned int valid:1;
 	unsigned int have_format:1;
 
 	uint32_t types;
@@ -57,6 +58,9 @@ struct port {
 	uint32_t n_buffers;
 
 	struct spa_list queue;
+
+	struct spa_list mix_link;
+	bool active;
 };
 
 struct impl {
@@ -77,10 +81,10 @@ struct impl {
 
 	struct spa_hook_list hooks;
 
-	uint32_t port_count;
-	uint32_t last_port;
 	struct port *in_ports[MAX_PORTS];
 	struct port out_ports[1];
+	struct spa_list port_list;
+	struct spa_list free_list;
 
 	struct spa_pod_control *mix_ctrl[MAX_PORTS];
 	struct spa_pod_sequence *mix_seq[MAX_PORTS];
@@ -89,12 +93,13 @@ struct impl {
 
 	unsigned int have_format:1;
 	unsigned int started:1;
+
+	struct spa_list mix_list;
 };
 
-#define PORT_VALID(p)                ((p) != NULL && (p)->valid)
 #define CHECK_ANY_IN(this,d,p)       ((d) == SPA_DIRECTION_INPUT && (p) == SPA_ID_INVALID)
-#define CHECK_FREE_IN_PORT(this,d,p) ((d) == SPA_DIRECTION_INPUT && (p) < MAX_PORTS && !PORT_VALID(this->in_ports[(p)]))
-#define CHECK_IN_PORT(this,d,p)      ((d) == SPA_DIRECTION_INPUT && (p) < MAX_PORTS && PORT_VALID(this->in_ports[(p)]))
+#define CHECK_FREE_IN_PORT(this,d,p) ((d) == SPA_DIRECTION_INPUT && (p) < MAX_PORTS && this->in_ports[(p)] == NULL)
+#define CHECK_IN_PORT(this,d,p)      ((d) == SPA_DIRECTION_INPUT && (p) < MAX_PORTS && this->in_ports[(p)] != NULL)
 #define CHECK_OUT_PORT(this,d,p)     ((d) == SPA_DIRECTION_OUTPUT && (p) == 0)
 #define CHECK_PORT(this,d,p)         (CHECK_OUT_PORT(this,d,p) || CHECK_IN_PORT (this,d,p))
 #define CHECK_PORT_ANY(this,d,p)     (CHECK_ANY_IN(this,d,p) || CHECK_PORT(this,d,p))
@@ -180,7 +185,7 @@ static int impl_node_add_listener(void *object,
 {
 	struct impl *this = object;
 	struct spa_hook_list save;
-	uint32_t i;
+	struct port *port;
 
 	spa_return_val_if_fail(this != NULL, -EINVAL);
 
@@ -188,10 +193,8 @@ static int impl_node_add_listener(void *object,
 
 	emit_node_info(this, true);
 	emit_port_info(this, GET_OUT_PORT(this, 0), true);
-	for (i = 0; i < this->last_port; i++) {
-		if (PORT_VALID(this->in_ports[i]))
-			emit_port_info(this, GET_IN_PORT(this, i), true);
-	}
+	spa_list_for_each(port, &this->port_list, link)
+		emit_port_info(this, port, true);
 
 	spa_hook_list_join(&this->hooks, &save);
 
@@ -206,6 +209,18 @@ impl_node_set_callbacks(void *object,
 	return 0;
 }
 
+static struct port *get_free_port(struct impl *this)
+{
+	struct port *port;
+	if (!spa_list_is_empty(&this->free_list)) {
+		port = spa_list_first(&this->free_list, struct port, link);
+		spa_list_remove(&port->link);
+	} else {
+		port = calloc(1, sizeof(struct port));
+	}
+	return port;
+}
+
 static int impl_node_add_port(void *object, enum spa_direction direction, uint32_t port_id,
 		const struct spa_dict *props)
 {
@@ -216,12 +231,8 @@ static int impl_node_add_port(void *object, enum spa_direction direction, uint32
 	spa_return_val_if_fail(CHECK_FREE_IN_PORT(this, direction, port_id), -EINVAL);
 
 	port = GET_IN_PORT (this, port_id);
-	if (port == NULL) {
-		port = calloc(1, sizeof(struct port));
-		if (port == NULL)
-			return -errno;
-		this->in_ports[port_id] = port;
-	}
+	if ((port = get_free_port(this)) == NULL)
+		return -errno;
 
 	port->direction = direction;
 	port->id = port_id;
@@ -242,12 +253,10 @@ static int impl_node_add_port(void *object, enum spa_direction direction, uint32
 	port->info.params = port->params;
 	port->info.n_params = 5;
 
-	this->port_count++;
-	if (this->last_port <= port_id)
-		this->last_port = port_id + 1;
-	port->valid = true;
+	this->in_ports[port_id] = port;
+	spa_list_append(&this->port_list, &port->link);
 
-	spa_log_debug(this->log, "%p: add port %d %d", this, port_id, this->last_port);
+	spa_log_debug(this->log, "%p: add port %d:%d", this, direction, port_id);
 	emit_port_info(this, port, true);
 
 	return 0;
@@ -263,25 +272,17 @@ impl_node_remove_port(void *object, enum spa_direction direction, uint32_t port_
 	spa_return_val_if_fail(CHECK_IN_PORT(this, direction, port_id), -EINVAL);
 
 	port = GET_IN_PORT (this, port_id);
+	this->in_ports[port_id] = NULL;
+	spa_list_remove(&port->link);
 
-	port->valid = false;
-	this->port_count--;
 	if (port->have_format && this->have_format) {
 		if (--this->n_formats == 0)
 			this->have_format = false;
 	}
 	spa_memzero(port, sizeof(struct port));
+	spa_list_append(&this->free_list, &port->link);
 
-	if (port_id + 1 == this->last_port) {
-		int i;
-
-		for (i = this->last_port - 1; i >= 0; i--)
-			if (GET_IN_PORT (this, i)->valid)
-				break;
-
-		this->last_port = i + 1;
-	}
-	spa_log_debug(this->log, "%p: remove port %d %d", this, port_id, this->last_port);
+	spa_log_debug(this->log, "%p: remove port %d:%d", this, direction, port_id);
 
 	spa_node_emit_port_info(&this->hooks, direction, port_id, NULL);
 
@@ -558,6 +559,7 @@ impl_node_port_use_buffers(void *object,
 }
 
 struct io_info {
+	struct impl *impl;
 	struct port *port;
 	void *data;
 	size_t size;
@@ -567,16 +569,28 @@ static int do_port_set_io(struct spa_loop *loop, bool async, uint32_t seq,
 		const void *data, size_t size, void *user_data)
 {
 	struct io_info *info = user_data;
-	if (info->size >= sizeof(struct spa_io_async_buffers)) {
-		struct spa_io_async_buffers *ab = info->data;
-		info->port->io[0] = &ab->buffers[0];
-		info->port->io[1] = &ab->buffers[1];
-	} else if (info->size >= sizeof(struct spa_io_buffers)) {
-		info->port->io[0] = info->data;
-		info->port->io[1] = info->data;
+	struct port *port = info->port;
+
+	if (info->data == NULL || info->size < sizeof(struct spa_io_buffers)) {
+		port->io[0] = NULL;
+		port->io[1] = NULL;
+		if (port->active) {
+			spa_list_remove(&port->mix_link);
+			port->active = false;
+		}
 	} else {
-		info->port->io[0] = NULL;
-		info->port->io[1] = NULL;
+		if (info->size >= sizeof(struct spa_io_async_buffers)) {
+			struct spa_io_async_buffers *ab = info->data;
+			port->io[0] = &ab->buffers[port->direction];
+			port->io[1] = &ab->buffers[port->direction^1];
+		} else {
+			port->io[0] = info->data;
+			port->io[1] = info->data;
+		}
+		if (!port->active) {
+			spa_list_append(&info->impl->mix_list, &port->mix_link);
+			port->active = true;
+		}
 	}
 	return 0;
 }
@@ -598,6 +612,7 @@ impl_node_port_set_io(void *object,
 	spa_return_val_if_fail(CHECK_PORT(this, direction, port_id), -EINVAL);
 
 	port = GET_PORT(this, direction, port_id);
+	info.impl = this;
 	info.port = port;
 	info.data = data;
 	info.size = size;
@@ -682,14 +697,14 @@ static inline bool control_needs_conversion(struct port *port, uint32_t type)
 static int impl_node_process(void *object)
 {
 	struct impl *this = object;
-	struct port *outport;
+	struct port *outport, *inport;
 	struct spa_io_buffers *outio;
-	uint32_t n_seq, i;
-        struct spa_pod_sequence **seq;
-        struct spa_pod_control **ctrl;
+	uint32_t n_seq;
+	struct spa_pod_sequence **seq;
+	struct spa_pod_control **ctrl;
 	struct spa_pod_builder builder;
 	struct spa_pod_frame f;
-        struct buffer *outb;
+	struct buffer *outb;
 	struct spa_data *d;
 	uint32_t cycle = this->position->clock.cycle & 1;
 
@@ -724,17 +739,10 @@ static int impl_node_process(void *object)
 	n_seq = 0;
 
 	/* collect all sequence pod on input ports */
-	for (i = 0; i < this->last_port; i++) {
-		struct port *inport = GET_IN_PORT(this, i);
-		struct spa_io_buffers *inio = NULL;
+	spa_list_for_each(inport, &this->mix_list, mix_link) {
+		struct spa_io_buffers *inio = inport->io[cycle];
 		void *pod;
 
-		if (SPA_UNLIKELY(!PORT_VALID(inport) || (inio = inport->io[cycle]) == NULL)) {
-			spa_log_trace_fp(this->log, "%p: skip input idx:%d valid:%d io:%p/%p/%d",
-					this, i, PORT_VALID(inport),
-					inport->io[0], inport->io[1], cycle);
-			continue;
-		}
 		if (inio->buffer_id >= inport->n_buffers ||
 		    inio->status != SPA_STATUS_HAVE_DATA) {
 			spa_log_trace_fp(this->log, "%p: skip input idx:%d "
@@ -775,7 +783,7 @@ static int impl_node_process(void *object)
 	/* merge sort all sequences into output buffer */
 	while (true) {
 		struct spa_pod_control *next = NULL;
-		uint32_t next_index = 0;
+		uint32_t i, next_index = 0;
 
 		for (i = 0; i < n_seq; i++) {
 			if (!spa_pod_control_is_inside(&seq[i]->body,
@@ -883,14 +891,18 @@ static int impl_get_interface(struct spa_handle *handle, const char *type, void
 static int impl_clear(struct spa_handle *handle)
 {
 	struct impl *this;
-	uint32_t i;
+	struct port *port;
 
 	spa_return_val_if_fail(handle != NULL, -EINVAL);
 
 	this = (struct impl *) handle;
 
-	for (i = 0; i < MAX_PORTS; i++)
-		free(this->in_ports[i]);
+	spa_list_insert_list(&this->free_list, &this->port_list);
+	spa_list_insert_list(&this->free_list, &this->mix_list);
+	spa_list_consume(port, &this->free_list, link) {
+		spa_list_remove(&port->link);
+		free(port);
+	}
 	return 0;
 }
 
@@ -939,6 +951,9 @@ impl_init(const struct spa_handle_factory *factory,
 	}
 
 	spa_hook_list_init(&this->hooks);
+	spa_list_init(&this->port_list);
+	spa_list_init(&this->free_list);
+	spa_list_init(&this->mix_list);
 
 	this->node.iface = SPA_INTERFACE_INIT(
 			SPA_TYPE_INTERFACE_Node,
@@ -951,7 +966,6 @@ impl_init(const struct spa_handle_factory *factory,
 	this->info.flags = SPA_NODE_FLAG_RT | SPA_NODE_FLAG_IN_DYNAMIC_PORTS;
 
 	port = GET_OUT_PORT(this, 0);
-	port->valid = true;
 	port->direction = SPA_DIRECTION_OUTPUT;
 	port->id = 0;
 	port->info = SPA_PORT_INFO_INIT();