[WIP] add media type for text, begin merge plugin

spa/include/spa/param/format.h

@@ -45,6 +45,7 @@ enum spa_media_type {
 	SPA_MEDIA_TYPE_binary,
 	SPA_MEDIA_TYPE_stream,
 	SPA_MEDIA_TYPE_application,
+	SPA_MEDIA_TYPE_text,
 };
 
 /** media subtype for SPA_TYPE_OBJECT_Format */
@@ -93,6 +94,7 @@ enum spa_media_subtype {
 	SPA_MEDIA_SUBTYPE_START_Application	= 0x60000,
 	SPA_MEDIA_SUBTYPE_control,		/**< control stream, data contains
 						  *  spa_pod_sequence with control info. */
+	SPA_MEDIA_SUBTYPE_START_Text	= 0x70000,
 };
 
 /** properties for audio SPA_TYPE_OBJECT_Format */
@@ -140,6 +142,9 @@ enum spa_format {
 	SPA_FORMAT_START_Stream = 0x50000,
 	/* Application Format keys */
 	SPA_FORMAT_START_Application = 0x60000,
+	/* Text Format keys */
+	SPA_FORMAT_START_Text = 0x70000,
+	SPA_FORMAT_TEXT_recordSeparator,	/**< (Int) % 256 */
 };
 
 #define SPA_KEY_FORMAT_DSP		"format.dsp"		/**< a predefined DSP format,

spa/include/spa/utils/names.h

@@ -47,6 +47,9 @@ extern "C" {
 
 #define SPA_NAME_SUPPORT_NODE_DRIVER	"support.node.driver"		/**< A dummy driver node */
 
+/* text mixer */
+#define SPA_NAME_TEXT_MIXER		"text.mixer"			/**< mixes text streams */
+
 /* control mixer */
 #define SPA_NAME_CONTROL_MIXER		"control.mixer"			/**< mixes control streams */
 

spa/plugins/meson.build

@@ -28,6 +28,9 @@ endif
 if not get_option('test').disabled()
   subdir('test')
 endif
+if not get_option('text').disabled()
+  subdir('text')
+endif
 if not get_option('videoconvert').disabled()
   subdir('videoconvert')
 endif

spa/plugins/text/meson.build

@@ -0,0 +1,7 @@
+text_sources = ['mixer.c', 'plugin.c', 'text-buffer.c']
+
+textlib = shared_library('spa-text',
+    text_sources,
+    include_directories : [spa_inc],
+    install : true,
+    install_dir : spa_plugindir / 'text')

spa/plugins/text/mixer.c

@@ -0,0 +1,829 @@
+/* Spa
+ *
+ * Copyright © 2019 Wim Taymans
+ * Copyright © 2021 Alain Zscheile
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+
+#include <spa/support/plugin.h>
+#include <spa/support/log.h>
+#include <spa/support/cpu.h>
+#include <spa/utils/list.h>
+#include <spa/utils/names.h>
+#include <spa/utils/string.h>
+#include <spa/node/node.h>
+#include <spa/node/utils.h>
+#include <spa/node/io.h>
+#include <spa/param/audio/format-utils.h>
+#include <spa/param/param.h>
+#include <spa/pod/filter.h>
+
+#include "text-buffer.h"
+
+#define NAME "text-mixer"
+
+#define MAX_BUFFERS     64
+#define MAX_PORTS       128
+
+struct buffer {
+	uint32_t id;
+#define BUFFER_FLAG_QUEUED	(1 << 0)
+	uint32_t flags;
+
+	struct spa_list link;
+	struct spa_buffer *buffer;
+};
+
+struct port {
+	uint32_t direction;
+	uint32_t id;
+
+	struct spa_io_buffers *io;
+
+	uint64_t info_all;
+	struct spa_port_info info;
+	struct spa_param_info params[8];
+
+	unsigned int valid:1;
+	unsigned int have_format:1;
+
+	struct buffer buffers[MAX_BUFFERS];
+	uint32_t n_buffers;
+
+	struct spa_list queue;
+
+	struct text_buffer line_cache; /**< caches the last incomplete line */
+};
+
+struct impl {
+	struct spa_handle handle;
+	struct spa_node node;
+
+	struct spa_log *log;
+
+	uint64_t info_all;
+	struct spa_node_info info;
+	struct spa_param_info params[8];
+
+	struct spa_hook_list hooks;
+
+	uint32_t port_count;
+	uint32_t last_port;
+	struct port in_ports[MAX_PORTS];
+	struct port out_ports[1];
+
+	int n_formats;
+
+	unsigned int have_format:1;
+	unsigned int started:1;
+};
+
+#define CHECK_FREE_IN_PORT(this,d,p) ((d) == SPA_DIRECTION_INPUT && (p) < MAX_PORTS && !this->in_ports[(p)].valid)
+#define CHECK_IN_PORT(this,d,p)      ((d) == SPA_DIRECTION_INPUT && (p) < MAX_PORTS && this->in_ports[(p)].valid)
+#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 GET_IN_PORT(this,p)          (&this->in_ports[p])
+#define GET_OUT_PORT(this,p)         (&this->out_ports[p])
+#define GET_PORT(this,d,p)           (d == SPA_DIRECTION_INPUT ? GET_IN_PORT(this,p) : GET_OUT_PORT(this,p))
+
+static int impl_node_enum_params(void *object, int seq,
+				 uint32_t id, uint32_t start, uint32_t num,
+				 const struct spa_pod *filter)
+{
+	return -ENOTSUP;
+}
+
+static int impl_node_set_param(void *object, uint32_t id, uint32_t flags,
+			       const struct spa_pod *param)
+{
+	return -ENOTSUP;
+}
+
+static int impl_node_set_io(void *object, uint32_t id, void *data, size_t size)
+{
+	return -ENOTSUP;
+}
+
+static int impl_node_send_command(void *object, const struct spa_command *command)
+{
+	struct impl *this = object;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(command != NULL, -EINVAL);
+
+	switch (SPA_NODE_COMMAND_ID(command)) {
+	case SPA_NODE_COMMAND_Start:
+		this->started = true;
+		break;
+	case SPA_NODE_COMMAND_Pause:
+		this->started = false;
+		break;
+	default:
+		return -ENOTSUP;
+	}
+	return 0;
+}
+
+static void emit_node_info(struct impl *this, bool full)
+{
+	uint64_t old = full ? this->info.change_mask : 0;
+	if (full)
+		this->info.change_mask = this->info_all;
+	if (this->info.change_mask) {
+		spa_node_emit_info(&this->hooks, &this->info);
+		this->info.change_mask = old;
+	}
+}
+
+static void emit_port_info(struct impl *this, struct port *port, bool full)
+{
+	uint64_t old = full ? port->info.change_mask : 0;
+	if (full)
+		port->info.change_mask = port->info_all;
+	if (port->info.change_mask) {
+		spa_node_emit_port_info(&this->hooks,
+				port->direction, port->id, &port->info);
+		port->info.change_mask = old;
+	}
+}
+
+static int impl_node_add_listener(void *object,
+		struct spa_hook *listener,
+		const struct spa_node_events *events,
+		void *data)
+{
+	struct impl *this = object;
+	struct spa_hook_list save;
+	uint32_t i;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+
+	spa_hook_list_isolate(&this->hooks, &save, listener, events, data);
+
+	emit_node_info(this, true);
+	emit_port_info(this, GET_OUT_PORT(this, 0), true);
+	for (i = 0; i < this->last_port; i++) {
+		if (this->in_ports[i].valid)
+			emit_port_info(this, GET_IN_PORT(this, i), true);
+	}
+
+	spa_hook_list_join(&this->hooks, &save);
+
+	return 0;
+}
+
+static int
+impl_node_set_callbacks(void *object,
+			const struct spa_node_callbacks *callbacks,
+			void *user_data)
+{
+	return 0;
+}
+
+static int impl_node_add_port(void *object, enum spa_direction direction, uint32_t port_id,
+		const struct spa_dict *props)
+{
+	struct impl *this = object;
+	struct port *port;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(CHECK_FREE_IN_PORT(this, direction, port_id), -EINVAL);
+
+	port = GET_IN_PORT (this, port_id);
+	port->direction = direction;
+	port->id = port_id;
+
+	spa_list_init(&port->queue);
+	port->info_all = SPA_PORT_CHANGE_MASK_FLAGS |
+			SPA_PORT_CHANGE_MASK_PARAMS;
+	port->info = SPA_PORT_INFO_INIT();
+	port->info.flags = SPA_PORT_FLAG_NO_REF |
+			   SPA_PORT_FLAG_DYNAMIC_DATA |
+			   SPA_PORT_FLAG_REMOVABLE;
+	port->params[0] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
+	port->params[1] = SPA_PARAM_INFO(SPA_PARAM_Meta, SPA_PARAM_INFO_READ);
+	port->params[2] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
+	port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+	port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+	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->line_cache = init_text_buffer(0);
+	port->valid = true;
+
+	spa_log_debug(this->log, NAME " %p: add port %d %d", this, port_id, this->last_port);
+	emit_port_info(this, port, true);
+
+	return 0;
+}
+
+static int
+impl_node_remove_port(void *object, enum spa_direction direction, uint32_t port_id)
+{
+	struct impl *this = object;
+	struct port *port;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(CHECK_IN_PORT(this, direction, port_id), -EINVAL);
+
+	port = GET_IN_PORT (this, port_id);
+
+	destroy_text_buffer(&port->line_cache);
+	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));
+
+	if (port_id == this->last_port - 1) {
+		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, NAME " %p: remove port %d %d", this, port_id, this->last_port);
+
+	spa_node_emit_port_info(&this->hooks, direction, port_id, NULL);
+
+	return 0;
+}
+
+static int port_enum_formats(void *object,
+			     enum spa_direction direction, uint32_t port_id,
+			     uint32_t index,
+			     struct spa_pod **param,
+			     struct spa_pod_builder *builder)
+{
+	switch (index) {
+	case 0:
+		*param = spa_pod_builder_add_object(builder,
+			SPA_TYPE_OBJECT_Format, SPA_PARAM_EnumFormat,
+			SPA_FORMAT_mediaType,      SPA_POD_Id(SPA_MEDIA_TYPE_text),
+			SPA_FORMAT_mediaSubtype,   SPA_POD_Id(SPA_MEDIA_SUBTYPE_unknown));
+		break;
+	default:
+		return 0;
+	}
+	return 1;
+}
+
+static int
+impl_node_port_enum_params(void *object, int seq,
+			   enum spa_direction direction, uint32_t port_id,
+			   uint32_t id, uint32_t start, uint32_t num,
+			   const struct spa_pod *filter)
+{
+	struct impl *this = object;
+	struct port *port;
+	struct spa_pod *param;
+	struct spa_pod_builder b = { 0 };
+	uint8_t buffer[1024];
+	struct spa_result_node_params result;
+	uint32_t count = 0;
+	int res;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(num != 0, -EINVAL);
+	spa_return_val_if_fail(CHECK_PORT(this, direction, port_id), -EINVAL);
+
+	port = GET_PORT(this, direction, port_id);
+
+	result.id = id;
+	result.next = start;
+next:
+	result.index = result.next++;
+
+	spa_pod_builder_init(&b, buffer, sizeof(buffer));
+
+	switch (id) {
+	case SPA_PARAM_EnumFormat:
+		if ((res = port_enum_formats(this, direction, port_id, result.index, &param, &b)) <= 0)
+			return res;
+		break;
+
+	case SPA_PARAM_Format:
+		if (!port->have_format)
+			return -EIO;
+		if ((res = port_enum_formats(this, direction, port_id, result.index, &param, &b)) <= 0)
+			return res;
+		break;
+
+	case SPA_PARAM_Buffers:
+		if (!port->have_format)
+			return -EIO;
+		if (result.index > 0)
+			return 0;
+
+		param = spa_pod_builder_add_object(&b,
+			SPA_TYPE_OBJECT_ParamBuffers, id,
+			SPA_PARAM_BUFFERS_buffers, SPA_POD_CHOICE_RANGE_Int(2, 1, MAX_BUFFERS),
+			SPA_PARAM_BUFFERS_blocks,  SPA_POD_Int(1),
+			SPA_PARAM_BUFFERS_size,    SPA_POD_CHOICE_RANGE_Int(4096, 512, INT32_MAX),
+			SPA_PARAM_BUFFERS_stride,  SPA_POD_Int(1),
+			SPA_PARAM_BUFFERS_align,   SPA_POD_Int(16));
+		break;
+
+	case SPA_PARAM_IO:
+		switch (result.index) {
+		case 0:
+			param = spa_pod_builder_add_object(&b,
+				SPA_TYPE_OBJECT_ParamIO, id,
+				SPA_PARAM_IO_id,   SPA_POD_Id(SPA_IO_Buffers),
+				SPA_PARAM_IO_size, SPA_POD_Int(sizeof(struct spa_io_buffers)));
+			break;
+		default:
+			return 0;
+		}
+		break;
+	default:
+		return -ENOENT;
+	}
+
+	if (spa_pod_filter(&b, &result.param, param, filter) < 0)
+		goto next;
+
+	spa_node_emit_result(&this->hooks, seq, 0, SPA_RESULT_TYPE_NODE_PARAMS, &result);
+
+	if (++count != num)
+		goto next;
+
+	return 0;
+}
+
+static int clear_buffers(struct impl *this, struct port *port)
+{
+	if (port->n_buffers > 0) {
+		spa_log_debug(this->log, NAME " %p: clear buffers %p", this, port);
+		port->n_buffers = 0;
+		spa_list_init(&port->queue);
+	}
+	return 0;
+}
+
+static int queue_buffer(struct impl *this, struct port *port, struct buffer *b)
+{
+	if (SPA_FLAG_IS_SET(b->flags, BUFFER_FLAG_QUEUED))
+		return -EINVAL;
+
+	spa_list_append(&port->queue, &b->link);
+	SPA_FLAG_SET(b->flags, BUFFER_FLAG_QUEUED);
+	spa_log_trace_fp(this->log, NAME " %p: queue buffer %d", this, b->id);
+	return 0;
+}
+
+static struct buffer *dequeue_buffer(struct impl *this, struct port *port)
+{
+	struct buffer *b;
+
+	if (spa_list_is_empty(&port->queue))
+		return NULL;
+
+	b = spa_list_first(&port->queue, struct buffer, link);
+	spa_list_remove(&b->link);
+	SPA_FLAG_CLEAR(b->flags, BUFFER_FLAG_QUEUED);
+	spa_log_trace_fp(this->log, NAME " %p: dequeue buffer %d", this, b->id);
+	return b;
+}
+
+static int port_set_format(void *object,
+			   enum spa_direction direction,
+			   uint32_t port_id,
+			   uint32_t flags,
+			   const struct spa_pod *format)
+{
+	struct impl *this = object;
+	struct port *port;
+	int res;
+
+	port = GET_PORT(this, direction, port_id);
+
+	if (format == NULL) {
+		if (port->have_format) {
+			port->have_format = false;
+			if (--this->n_formats == 0)
+				this->have_format = false;
+			clear_buffers(this, port);
+		}
+	} else {
+		uint32_t media_type, media_subtype;
+		if ((res = spa_format_parse(format, &media_type, &media_subtype)) < 0)
+			return res;
+
+		if (media_type != SPA_MEDIA_TYPE_text ||
+		    media_subtype != SPA_MEDIA_SUBTYPE_unknown)
+			return -EINVAL;
+
+		this->have_format = true;
+
+		if (!port->have_format) {
+			this->n_formats++;
+			port->have_format = true;
+			spa_log_debug(this->log, NAME " %p: set format on port %d:%d",
+					this, direction, port_id);
+		}
+	}
+	port->info.change_mask |= SPA_PORT_CHANGE_MASK_PARAMS;
+	if (port->have_format) {
+		port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_READWRITE);
+		port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, SPA_PARAM_INFO_READ);
+	} else {
+		port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+		port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+	}
+	emit_port_info(this, port, false);
+
+	return 0;
+}
+
+
+static int
+impl_node_port_set_param(void *object,
+			 enum spa_direction direction, uint32_t port_id,
+			 uint32_t id, uint32_t flags,
+			 const struct spa_pod *param)
+{
+	struct impl *this = object;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(CHECK_PORT(this, direction, port_id), -EINVAL);
+
+	if (id == SPA_PARAM_Format) {
+		return port_set_format(this, direction, port_id, flags, param);
+	}
+	else
+		return -ENOENT;
+}
+
+static int
+impl_node_port_use_buffers(void *object,
+			   enum spa_direction direction,
+			   uint32_t port_id,
+			   uint32_t flags,
+			   struct spa_buffer **buffers,
+			   uint32_t n_buffers)
+{
+	struct impl *this = object;
+	struct port *port;
+	uint32_t i;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(CHECK_PORT(this, direction, port_id), -EINVAL);
+
+	port = GET_PORT(this, direction, port_id);
+
+	spa_log_debug(this->log, NAME " %p: use buffers %d on port %d:%d",
+			this, n_buffers, direction, port_id);
+
+	spa_return_val_if_fail(port->have_format, -EIO);
+
+	clear_buffers(this, port);
+
+	for (i = 0; i < n_buffers; i++) {
+		struct buffer *b;
+		struct spa_data *d = buffers[i]->datas;
+
+		b = &port->buffers[i];
+		b->buffer = buffers[i];
+		b->flags = 0;
+		b->id = i;
+
+		if (d[0].data == NULL) {
+			spa_log_error(this->log, NAME " %p: invalid memory on buffer %d", this, i);
+			return -EINVAL;
+		}
+		if (direction == SPA_DIRECTION_OUTPUT)
+			queue_buffer(this, port, b);
+	}
+	port->n_buffers = n_buffers;
+
+	return 0;
+}
+
+static int
+impl_node_port_set_io(void *object,
+		      enum spa_direction direction, uint32_t port_id,
+		      uint32_t id, void *data, size_t size)
+{
+	struct impl *this = object;
+	struct port *port;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(CHECK_PORT(this, direction, port_id), -EINVAL);
+
+	port = GET_PORT(this, direction, port_id);
+
+	spa_log_debug(this->log, NAME " %p: port %d:%d io %d %p/%zd", this,
+			direction, port_id, id, data, size);
+
+	switch (id) {
+	case SPA_IO_Buffers:
+		port->io = data;
+		break;
+	default:
+		return -ENOENT;
+	}
+	return 0;
+}
+
+static int impl_node_port_reuse_buffer(void *object, uint32_t port_id, uint32_t buffer_id)
+{
+	struct impl *this = object;
+	struct port *port;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(CHECK_PORT(this, SPA_DIRECTION_OUTPUT, port_id), -EINVAL);
+	port = GET_OUT_PORT(this, 0);
+
+	if (buffer_id >= port->n_buffers)
+		return -EINVAL;
+
+	return queue_buffer(this, port, &port->buffers[buffer_id]);
+}
+
+static int impl_node_process(void *object)
+{
+	struct impl *this = object;
+	struct port *outport;
+	struct spa_io_buffers *outio;
+	uint32_t n_seq, i;
+	char   **inpbufs;
+	struct buffer *outb;
+	char   *d;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+
+	outport = GET_OUT_PORT(this, 0);
+	outio = outport->io;
+	spa_return_val_if_fail(outio != NULL, -EIO);
+
+	spa_log_trace_fp(this->log, NAME " %p: status %p %d %d",
+			this, outio, outio->status, outio->buffer_id);
+
+	if (outio->status == SPA_STATUS_HAVE_DATA)
+		return outio->status;
+
+	/* recycle */
+	if (outio->buffer_id < outport->n_buffers) {
+		queue_buffer(this, outport, &outport->buffers[outio->buffer_id]);
+		outio->buffer_id = SPA_ID_INVALID;
+	}
+
+	/* get output buffer */
+	if ((outb = dequeue_buffer(this, outport)) == NULL) {
+		spa_log_trace(this->log, NAME " %p: out of buffers", this);
+		return -EPIPE;
+	}
+
+	inpbufs = alloca(MAX_PORTS * sizeof(char *));
+	n_seq = 0;
+
+	/* collect all data 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;
+		char *curdat = NULL;
+
+		if (!inport->valid ||
+		    (inio = inport->io) == NULL ||
+		    in_port->queued_byted == 0)
+			continue;
+
+		if (inio->buffer_id >= inport->n_buffers ||
+		    inio->status != SPA_STATUS_HAVE_DATA) {
+			spa_log_trace_fp(this->log, NAME " %p: skip input idx:%d "
+					"io:%p status:%d buf_id:%d n_buffers:%d", this,
+				i, inio,
+				inio ? inio->status : -1,
+				inio ? inio->buffer_id : SPA_ID_INVALID,
+				inport->n_buffers);
+			continue;
+		}
+
+		spa_log_trace_fp(this->log, NAME " %p: mix input %d %p->%p %d %d", this,
+				i, inio, outio, inio->status, inio->buffer_id);
+
+		d = inport->buffers[inio->buffer_id].buffer->datas;
+
+		/* validate bounds */
+		if (d->chunk->offset + d->chunk->size > d->maxsize)
+			continue;
+
+		/*if ((pod = spa_pod_from_data(d->data, d->maxsize,
+				d->chunk->offset, d->chunk->size)) == NULL)
+			continue;*/
+
+		curdat = SPA_PTROFF((d->data), (d->chunk->offset), char);
+		/* fast path, no cached data */
+		if (!inport->line_cache.length && curdat[d->chunk->size] == ) {
+			
+		}
+
+
+		inio->status = SPA_STATUS_NEED_DATA;
+		n_seq++;
+	}
+
+	d = outb->buffer->datas;
+
+	/* prepare to write into output */
+	spa_pod_builder_init(&builder, d->data, d->maxsize);
+	spa_pod_builder_push_sequence(&builder, &f, 0);
+
+	/* merge sort all sequences into output buffer */
+	while (true) {
+		struct spa_pod_control *next = NULL;
+		uint32_t next_index = 0;
+
+		for (i = 0; i < n_seq; i++) {
+			if (!spa_pod_control_is_inside(&seq[i]->body,
+					SPA_POD_BODY_SIZE(seq[i]), ctrl[i]))
+				continue;
+
+			if (next == NULL || ctrl[i]->offset < next->offset) {
+				next = ctrl[i];
+				next_index = i;
+			}
+		}
+		if (next == NULL)
+			break;
+
+		spa_pod_builder_control(&builder, next->offset, next->type);
+		spa_pod_builder_primitive(&builder, &next->value);
+
+		ctrl[next_index] = spa_pod_control_next(ctrl[next_index]);
+	}
+	spa_pod_builder_pop(&builder, &f);
+
+	d->chunk->offset = 0;
+	d->chunk->size = builder.state.offset;
+	d->chunk->stride = 1;
+	d->chunk->flags = 0;
+
+	outio->buffer_id = outb->id;
+	outio->status = SPA_STATUS_HAVE_DATA;
+
+	return SPA_STATUS_HAVE_DATA | SPA_STATUS_NEED_DATA;
+}
+
+static const struct spa_node_methods impl_node = {
+	SPA_VERSION_NODE_METHODS,
+	.add_listener = impl_node_add_listener,
+	.set_callbacks = impl_node_set_callbacks,
+	.enum_params = impl_node_enum_params,
+	.set_param = impl_node_set_param,
+	.set_io = impl_node_set_io,
+	.send_command = impl_node_send_command,
+	.add_port = impl_node_add_port,
+	.remove_port = impl_node_remove_port,
+	.port_enum_params = impl_node_port_enum_params,
+	.port_set_param = impl_node_port_set_param,
+	.port_use_buffers = impl_node_port_use_buffers,
+	.port_set_io = impl_node_port_set_io,
+	.port_reuse_buffer = impl_node_port_reuse_buffer,
+	.process = impl_node_process,
+};
+
+static int impl_get_interface(struct spa_handle *handle, const char *type, void **interface)
+{
+	struct impl *this;
+
+	spa_return_val_if_fail(handle != NULL, -EINVAL);
+	spa_return_val_if_fail(interface != NULL, -EINVAL);
+
+	this = (struct impl *) handle;
+
+	if (spa_streq(type, SPA_TYPE_INTERFACE_Node))
+		*interface = &this->node;
+	else
+		return -ENOENT;
+
+	return 0;
+}
+
+static int impl_clear(struct spa_handle *handle)
+{
+	return 0;
+}
+
+static size_t
+impl_get_size(const struct spa_handle_factory *factory,
+	      const struct spa_dict *params)
+{
+	return sizeof(struct impl);
+}
+
+static int
+impl_init(const struct spa_handle_factory *factory,
+	  struct spa_handle *handle,
+	  const struct spa_dict *info,
+	  const struct spa_support *support,
+	  uint32_t n_support)
+{
+	struct impl *this;
+	struct port *port;
+
+	spa_return_val_if_fail(factory != NULL, -EINVAL);
+	spa_return_val_if_fail(handle != NULL, -EINVAL);
+
+	handle->get_interface = impl_get_interface;
+	handle->clear = impl_clear;
+
+	this = (struct impl *) handle;
+
+	this->log = spa_support_find(support, n_support, SPA_TYPE_INTERFACE_Log);
+
+	spa_hook_list_init(&this->hooks);
+
+	this->node.iface = SPA_INTERFACE_INIT(
+			SPA_TYPE_INTERFACE_Node,
+			SPA_VERSION_NODE,
+			&impl_node, this);
+	this->info = SPA_NODE_INFO_INIT();
+	this->info.max_input_ports = MAX_PORTS;
+	this->info.max_output_ports = 1;
+	this->info.change_mask |= SPA_NODE_CHANGE_MASK_FLAGS;
+	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();
+	port->info.change_mask |= SPA_PORT_CHANGE_MASK_FLAGS;
+	port->info.flags = SPA_PORT_FLAG_DYNAMIC_DATA;
+	port->info.change_mask |= SPA_PORT_CHANGE_MASK_PARAMS;
+	port->params[0] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
+	port->params[1] = SPA_PARAM_INFO(SPA_PARAM_Meta, SPA_PARAM_INFO_READ);
+	port->params[2] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
+	port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+	port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+	port->info.params = port->params;
+	port->info.n_params = 5;
+
+	spa_list_init(&port->queue);
+
+	return 0;
+}
+
+static const struct spa_interface_info impl_interfaces[] = {
+	{SPA_TYPE_INTERFACE_Node,},
+};
+
+static int
+impl_enum_interface_info(const struct spa_handle_factory *factory,
+			 const struct spa_interface_info **info,
+			 uint32_t *index)
+{
+	spa_return_val_if_fail(factory != NULL, -EINVAL);
+	spa_return_val_if_fail(info != NULL, -EINVAL);
+	spa_return_val_if_fail(index != NULL, -EINVAL);
+
+	switch (*index) {
+	case 0:
+		*info = &impl_interfaces[*index];
+		break;
+	default:
+		return 0;
+	}
+	(*index)++;
+	return 1;
+}
+
+const struct spa_handle_factory spa_control_mixer_factory = {
+	SPA_VERSION_HANDLE_FACTORY,
+	SPA_NAME_CONTROL_MIXER,
+	NULL,
+	impl_get_size,
+	impl_init,
+	impl_enum_interface_info,
+};

spa/plugins/text/plugin.c

@@ -0,0 +1,46 @@
+/* Spa Text plugin
+ *
+ * Copyright © 2018 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <errno.h>
+
+#include <spa/support/plugin.h>
+
+extern const struct spa_handle_factory spa_text_mixer_factory;
+
+SPA_EXPORT
+int spa_handle_factory_enum(const struct spa_handle_factory **factory, uint32_t *index)
+{
+	spa_return_val_if_fail(factory != NULL, -EINVAL);
+	spa_return_val_if_fail(index != NULL, -EINVAL);
+
+	switch (*index) {
+	case 0:
+		*factory = &spa_text_mixer_factory;
+		break;
+	default:
+		return 0;
+	}
+	(*index)++;
+	return 1;
+}

spa/plugins/text/text-buffer.c

@@ -0,0 +1,93 @@
+/* Spa
+ *
+ * Copyright © 2021 Alain Zscheile
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "text-buffer.h"
+#include <stdlib.h>
+#include <string.h>
+
+#define TXTBUF_SHRINK_FACTOR 10
+
+struct text_buffer init_text_buffer(size_t initial_cap)
+{
+	struct text_buffer ret;
+	ret.ptr = NULL;
+	ret.length = 0;
+
+	if (initial_cap != NULL) {
+		ret.ptr = calloc(initial_cap, sizeof(char));
+	}
+
+	ret.capacity = ret.ptr ? initial_cap : 0;
+	return ret;
+}
+
+void destroy_text_buffer(struct text_buffer * b)
+{
+	if (b == NULL)
+		return;
+
+	if (b->ptr)
+		free(b->ptr);
+
+	b->ptr = NULL;
+	b->capacity = 0;
+	b->length = 0;
+}
+
+bool text_buffer_resize(struct text_buffer * b, size_t newlen)
+{
+	if ((b->length != newlen) && (b->capacity < newlen || (b->capacity / TXTBUF_SHRINK_FACTOR) > newlen)) {
+		char * nptr = realloc(b->ptr, newlen);
+		if (nptr == NULL) {
+			/* memory allocation failed */
+			return false;
+		}
+		b->ptr = nptr;
+	}
+	b->length = newlen;
+	return true;
+}
+
+bool text_buffer_append(struct text_buffer * b, size_t dlen, char * data)
+{
+	if (!text_buffer_resize(b, b->length + dlen))
+		return false;
+
+	memcpy(b->ptr + b->length, data, dlen);
+	return true;
+}
+
+void text_buffer_shift (struct text_buffer * b, size_t slen)
+{
+	if (slen > b->length) {
+		b->length = 0;
+		return;
+	}
+
+	if (!slen)
+		return;
+
+	memmove(b->ptr, b->ptr + slen, b->length);
+	b->length -= slen;
+}

spa/plugins/text/text-buffer.h

@@ -0,0 +1,45 @@
+/* Spa
+ *
+ * Copyright © 2021 Alain Zscheile
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <stdbool.h>
+#include <inttypes.h>
+
+struct text_buffer {
+	size_t capacity;
+	size_t length;
+	char * ptr; /**< not null terminated byte array */
+};
+
+struct text_buffer init_text_buffer(size_t initial_cap);
+void destroy_text_buffer(struct text_buffer * b);
+
+/* the following functions require the first (text_buffer *) argument to be non-NULL */
+
+bool text_buffer_resize(struct text_buffer * b, size_t newlen);
+
+/* appends the byte array given in @data with length @dlen to @b */
+bool text_buffer_append(struct text_buffer * b, size_t dlen, char * data);
+
+/* shifts the content of @b @slen bytes to the left, thereby discarding the first @slen bytes */
+void text_buffer_shift (struct text_buffer * b, size_t slen);

src/pipewire/impl-port.c

@@ -623,6 +623,10 @@ static int setup_mixer(struct pw_impl_port *port, const struct spa_pod *param)
 		}
 		break;
 
+	case SPA_MEDIA_TYPE_text:
+		fallback_lib = "text/libspa-text";
+		factory_name = SPA_NAME_TEXT_MIXER;
+
 	default:
 		return -ENOTSUP;
 	}

src/pipewire/stream.c

@@ -1573,6 +1573,8 @@ static const char *get_media_class(struct stream *impl)
 			return "Midi";
 		}
 		return "Data";
+	case SPA_MEDIA_TYPE_text:
+		return "Text";
 	default:
 		return "Unknown";
 	}