gstreamer/gst-libs/gst/rtp/gstrtphdrext.c

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/* GStreamer
* Copyright (C) <2012> Wim Taymans <wim.taymans@gmail.com>
* Copyright (C) <2020> Matthew Waters <matthew@centricular.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/**
2015-06-19 01:02:48 +00:00
* SECTION:gstrtphdrext
* @title: GstRtphdrext
* @short_description: Helper methods for dealing with RTP header extensions
* @see_also: #GstRTPBasePayload, #GstRTPBaseDepayload, gstrtpbuffer
*
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "gstrtphdrext.h"
#include <stdlib.h>
#include <string.h>
GST_DEBUG_CATEGORY_STATIC (rtphderext_debug);
#define GST_CAT_DEFAULT (rtphderext_debug)
#define MAX_RTP_EXT_ID 256
typedef struct
{
guint ext_id;
gboolean wants_update_non_rtp_src_caps;
} GstRTPHeaderExtensionPrivate;
/**
* gst_rtp_hdrext_set_ntp_64:
* @data: the data to write to
* @size: the size of @data
* @ntptime: the NTP time
*
* Writes the NTP time in @ntptime to the format required for the NTP-64 header
* extension. @data must hold at least #GST_RTP_HDREXT_NTP_64_SIZE bytes.
*
* Returns: %TRUE on success.
*/
gboolean
gst_rtp_hdrext_set_ntp_64 (gpointer data, guint size, guint64 ntptime)
{
g_return_val_if_fail (data != NULL, FALSE);
g_return_val_if_fail (size >= GST_RTP_HDREXT_NTP_64_SIZE, FALSE);
GST_WRITE_UINT64_BE (data, ntptime);
return TRUE;
}
/**
* gst_rtp_hdrext_get_ntp_64:
* @data: (array length=size) (element-type guint8): the data to read from
* @size: the size of @data
* @ntptime: (out): the result NTP time
*
* Reads the NTP time from the @size NTP-64 extension bytes in @data and store the
* result in @ntptime.
*
* Returns: %TRUE on success.
*/
gboolean
gst_rtp_hdrext_get_ntp_64 (gpointer data, guint size, guint64 * ntptime)
{
g_return_val_if_fail (data != NULL, FALSE);
g_return_val_if_fail (size >= GST_RTP_HDREXT_NTP_64_SIZE, FALSE);
if (ntptime)
*ntptime = GST_READ_UINT64_BE (data);
return TRUE;
}
/**
* gst_rtp_hdrext_set_ntp_56:
* @data: the data to write to
* @size: the size of @data
* @ntptime: the NTP time
*
* Writes the NTP time in @ntptime to the format required for the NTP-56 header
* extension. @data must hold at least #GST_RTP_HDREXT_NTP_56_SIZE bytes.
*
* Returns: %TRUE on success.
*/
gboolean
gst_rtp_hdrext_set_ntp_56 (gpointer data, guint size, guint64 ntptime)
{
guint8 *d = data;
gint i;
g_return_val_if_fail (data != NULL, FALSE);
g_return_val_if_fail (size >= GST_RTP_HDREXT_NTP_56_SIZE, FALSE);
for (i = 0; i < 7; i++) {
d[6 - i] = ntptime & 0xff;
ntptime >>= 8;
}
return TRUE;
}
/**
* gst_rtp_hdrext_get_ntp_56:
* @data: (array length=size) (element-type guint8): the data to read from
* @size: the size of @data
* @ntptime: (out): the result NTP time
*
* Reads the NTP time from the @size NTP-56 extension bytes in @data and store the
* result in @ntptime.
*
* Returns: %TRUE on success.
*/
gboolean
gst_rtp_hdrext_get_ntp_56 (gpointer data, guint size, guint64 * ntptime)
{
guint8 *d = data;
g_return_val_if_fail (data != NULL, FALSE);
g_return_val_if_fail (size >= GST_RTP_HDREXT_NTP_56_SIZE, FALSE);
if (ntptime) {
gint i;
*ntptime = 0;
for (i = 0; i < 7; i++) {
*ntptime <<= 8;
2012-09-24 11:08:46 +00:00
*ntptime |= d[i];
}
}
return TRUE;
}
#define gst_rtp_header_extension_parent_class parent_class
G_DEFINE_TYPE_EXTENDED (GstRTPHeaderExtension, gst_rtp_header_extension,
GST_TYPE_ELEMENT, G_TYPE_FLAG_ABSTRACT,
G_ADD_PRIVATE (GstRTPHeaderExtension)
GST_DEBUG_CATEGORY_INIT (GST_CAT_DEFAULT, "rtphdrext", 0,
"RTP Header Extensions")
);
/**
* gst_rtp_header_extension_class_set_uri:
* @klass: the #GstRTPHeaderExtensionClass
* @uri: the RTP Header extension uri for @klass
*
* Set the URI for this RTP header extension implementation.
*
* Since: 1.20
*/
void
gst_rtp_header_extension_class_set_uri (GstRTPHeaderExtensionClass * klass,
const gchar * uri)
{
GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
gst_element_class_add_static_metadata (element_class,
GST_RTP_HEADER_EXTENSION_URI_METADATA_KEY, uri);
}
static void
gst_rtp_header_extension_class_init (GstRTPHeaderExtensionClass * klass)
{
}
static void
gst_rtp_header_extension_init (GstRTPHeaderExtension * ext)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
priv->ext_id = G_MAXUINT32;
}
/**
* gst_rtp_header_extension_get_uri:
* @ext: a #GstRTPHeaderExtension
*
* Returns: the RTP extension URI for this object
*
* Since: 1.20
*/
const gchar *
gst_rtp_header_extension_get_uri (GstRTPHeaderExtension * ext)
{
GstRTPHeaderExtensionClass *klass;
GstElementClass *element_class;
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), NULL);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
element_class = GST_ELEMENT_CLASS (klass);
return gst_element_class_get_metadata (element_class,
GST_RTP_HEADER_EXTENSION_URI_METADATA_KEY);
}
/**
* gst_rtp_header_extension_get_supported_flags:
* @ext: a #GstRTPHeaderExtension
*
* Returns: the flags supported by this instance of @ext
*
* Since: 1.20
*/
GstRTPHeaderExtensionFlags
gst_rtp_header_extension_get_supported_flags (GstRTPHeaderExtension * ext)
{
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), 0);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
g_return_val_if_fail (klass->get_supported_flags != NULL, 0);
return klass->get_supported_flags (ext);
}
/**
* gst_rtp_header_extension_get_max_size:
* @ext: a #GstRTPHeaderExtension
* @input_meta: a #GstBuffer
*
* This is used to know how much data a certain header extension will need for
* both allocating the resulting data, and deciding how much payload data can
* be generated.
*
* Implementations should return as accurate a value as is possible using the
* information given in the input @buffer.
*
* Returns: the maximum size of the data written by this extension
*
* Since: 1.20
*/
gsize
gst_rtp_header_extension_get_max_size (GstRTPHeaderExtension * ext,
const GstBuffer * input_meta)
{
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_BUFFER (input_meta), 0);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), 0);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
g_return_val_if_fail (klass->get_max_size != NULL, 0);
return klass->get_max_size (ext, input_meta);
}
/**
* gst_rtp_header_extension_write:
* @ext: a #GstRTPHeaderExtension
* @input_meta: the input #GstBuffer to read information from if necessary
* @write_flags: #GstRTPHeaderExtensionFlags for how the extension should
* be written
* @output: output RTP #GstBuffer
* @data: (array length=size): location to write the rtp header extension into
* @size: size of @data
*
* Writes the RTP header extension to @data using information available from
* the @input_meta. @data will be sized to be at least the value returned
* from gst_rtp_header_extension_get_max_size().
*
* Returns: the size of the data written, < 0 on failure
*
* Since: 1.20
*/
gsize
gst_rtp_header_extension_write (GstRTPHeaderExtension * ext,
const GstBuffer * input_meta, GstRTPHeaderExtensionFlags write_flags,
GstBuffer * output, guint8 * data, gsize size)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_BUFFER (input_meta), -1);
g_return_val_if_fail (GST_IS_BUFFER (output), -1);
g_return_val_if_fail (gst_buffer_is_writable (output), -1);
g_return_val_if_fail (data != NULL, -1);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), -1);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, -1);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
g_return_val_if_fail (klass->write != NULL, -1);
return klass->write (ext, input_meta, write_flags, output, data, size);
}
/**
* gst_rtp_header_extension_read:
* @ext: a #GstRTPHeaderExtension
* @read_flags: #GstRTPHeaderExtensionFlags for how the extension should
* be written
* @data: (array length=size): location to read the rtp header extension from
* @size: size of @data
* @buffer: a #GstBuffer to modify if necessary
*
* Read the RTP header extension from @data.
*
* Returns: whether the extension could be read from @data
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_read (GstRTPHeaderExtension * ext,
GstRTPHeaderExtensionFlags read_flags, const guint8 * data, gsize size,
GstBuffer * buffer)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_BUFFER (buffer), FALSE);
g_return_val_if_fail (gst_buffer_is_writable (buffer), FALSE);
g_return_val_if_fail (data != NULL, FALSE);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), FALSE);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, FALSE);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
g_return_val_if_fail (klass->read != NULL, FALSE);
return klass->read (ext, read_flags, data, size, buffer);
}
/**
* gst_rtp_header_extension_get_id:
* @ext: a #GstRTPHeaderExtension
*
* Returns: the RTP extension id configured on @ext
*
* Since: 1.20
*/
guint
gst_rtp_header_extension_get_id (GstRTPHeaderExtension * ext)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), 0);
return priv->ext_id;
}
/**
* gst_rtp_header_extension_set_id:
* @ext: a #GstRTPHeaderExtension
* @ext_id: The id of this extension
*
* sets the RTP extension id on @ext
*
* Since: 1.20
*/
void
gst_rtp_header_extension_set_id (GstRTPHeaderExtension * ext, guint ext_id)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
g_return_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext));
g_return_if_fail (ext_id < MAX_RTP_EXT_ID);
priv->ext_id = ext_id;
}
/**
* gst_rtp_header_extension_set_attributes_from_caps:
* @ext: a #GstRTPHeaderExtension
* @caps: the #GstCaps to configure this extension with
*
* gst_rtp_header_extension_set_id() must have been called with a valid
* extension id that is contained in these caps.
*
* The only current known caps format is based on the SDP standard as produced
* by gst_sdp_media_attributes_to_caps().
*
* Returns: whether the @caps could be successfully set on @ext.
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_set_attributes_from_caps (GstRTPHeaderExtension * ext,
const GstCaps * caps)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
GstRTPHeaderExtensionClass *klass;
GstStructure *structure;
gchar *field_name;
g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);
g_return_val_if_fail (gst_caps_is_fixed (caps), FALSE);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), FALSE);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, FALSE);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
g_return_val_if_fail (klass->set_attributes_from_caps != NULL, FALSE);
structure = gst_caps_get_structure (caps, 0);
g_return_val_if_fail (structure != NULL, FALSE);
field_name = g_strdup_printf ("extmap-%u", priv->ext_id);
g_return_val_if_fail (gst_structure_has_field (structure, field_name), FALSE);
g_free (field_name);
return klass->set_attributes_from_caps (ext, caps);
}
/**
* gst_rtp_header_extension_wants_update_non_rtp_src_caps:
* @ext: a #GstRTPHeaderExtension
*
* Call this function after gst_rtp_header_extension_read() to check if
* the depayloader's src caps need updating with data received in the last RTP
* packet.
*
* Returns: Whether @ext wants to update depayloader's src caps.
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_wants_update_non_rtp_src_caps (GstRTPHeaderExtension *
ext)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), FALSE);
return priv->wants_update_non_rtp_src_caps;
}
/**
* gst_rtp_header_extension_set_wants_update_non_rtp_src_caps:
* @ext: a #GstRTPHeaderExtension
* @state: TRUE if caps update is needed
*
* Call this function in a subclass from #GstRTPHeaderExtensionClass::read to
* tell the depayloader whether the data just parsed from RTP packet require
* updating its src (non-RTP) caps. If @state is TRUE, #GstRTPBaseDepayload will
* eventually invoke gst_rtp_header_extension_update_non_rtp_src_caps() to
* have the caps update applied. Applying the update also flips the internal
* "wants update" flag back to FALSE.
*
* Since: 1.20
*/
void gst_rtp_header_extension_set_wants_update_non_rtp_src_caps
(GstRTPHeaderExtension * ext, gboolean state)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
g_return_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext));
priv->wants_update_non_rtp_src_caps = state;
}
/**
* gst_rtp_header_extension_set_non_rtp_sink_caps:
* @ext: a #GstRTPHeaderExtension
* @caps: sink #GstCaps
*
* Passes RTP payloader's sink (i.e. not payloaded) @caps to the header
* extension.
*
* Returns: Whether @caps could be read successfully
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_set_non_rtp_sink_caps (GstRTPHeaderExtension * ext,
const GstCaps * caps)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), FALSE);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, FALSE);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
if (klass->set_non_rtp_sink_caps) {
return klass->set_non_rtp_sink_caps (ext, caps);
}
return TRUE;
}
/**
* gst_rtp_header_extension_update_non_rtp_src_caps:
* @ext: a #GstRTPHeaderExtension
* @caps: src #GstCaps to modify
*
* Updates depayloader src caps based on the information received in RTP header.
* @caps must be writable as this function may modify them.
*
* Returns: whether @caps were modified successfully
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_update_non_rtp_src_caps (GstRTPHeaderExtension * ext,
GstCaps * caps)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);
g_return_val_if_fail (gst_caps_is_writable (caps), FALSE);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), FALSE);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, FALSE);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
priv->wants_update_non_rtp_src_caps = FALSE;
if (klass->update_non_rtp_src_caps) {
return klass->update_non_rtp_src_caps (ext, caps);
}
return TRUE;
}
/**
* gst_rtp_header_extension_set_caps_from_attributes:
* @ext: a #GstRTPHeaderExtension
* @caps: writable #GstCaps to modify
*
* gst_rtp_header_extension_set_id() must have been called with a valid
* extension id that is contained in these caps.
*
* The only current known caps format is based on the SDP standard as produced
* by gst_sdp_media_attributes_to_caps().
*
* Returns: whether the configured attributes on @ext can successfully be set on
* @caps
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_set_caps_from_attributes (GstRTPHeaderExtension * ext,
GstCaps * caps)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
GstRTPHeaderExtensionClass *klass;
g_return_val_if_fail (GST_IS_CAPS (caps), FALSE);
g_return_val_if_fail (gst_caps_is_writable (caps), FALSE);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), FALSE);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, FALSE);
klass = GST_RTP_HEADER_EXTENSION_GET_CLASS (ext);
g_return_val_if_fail (klass->set_caps_from_attributes != NULL, FALSE);
return klass->set_caps_from_attributes (ext, caps);
}
/**
* gst_rtp_header_extension_get_sdp_caps_field_name:
* @ext: the #GstRTPHeaderExtension
*
* Returns: (transfer full): the #GstStructure field name used in SDP-like #GstCaps for this @ext configuration
*
* Since: 1.20
*/
gchar *
gst_rtp_header_extension_get_sdp_caps_field_name (GstRTPHeaderExtension * ext)
{
GstRTPHeaderExtensionPrivate *priv =
gst_rtp_header_extension_get_instance_private (ext);
g_return_val_if_fail (GST_IS_RTP_HEADER_EXTENSION (ext), NULL);
g_return_val_if_fail (priv->ext_id <= MAX_RTP_EXT_ID, NULL);
return g_strdup_printf ("extmap-%u", priv->ext_id);
}
/**
* gst_rtp_header_extension_set_attributes_from_caps_simple_sdp:
* @ext: the #GstRTPHeaderExtension
* @caps: #GstCaps to read attributes from
*
* Helper implementation for GstRTPExtensionClass::set_attributes_from_caps
* that retrieves the configured extension id and checks that the
* corresponding field in the sdp caps is configured for this extension uri.
* Requires that the extension does not have any attributes or direction
* advertised in the caps.
*
* Returns: whether the attributes in the @caps could be set on @ext successfully
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_set_attributes_from_caps_simple_sdp
(GstRTPHeaderExtension * ext, const GstCaps * caps) {
gchar *field_name = gst_rtp_header_extension_get_sdp_caps_field_name (ext);
GstStructure *s = gst_caps_get_structure (caps, 0);
const gchar *ext_uri;
if (!(ext_uri = gst_structure_get_string (s, field_name)))
goto error;
if (g_strcmp0 (ext_uri, gst_rtp_header_extension_get_uri (ext)) != 0)
goto error;
g_free (field_name);
return TRUE;
error:
g_free (field_name);
return FALSE;
}
/**
* gst_rtp_header_extension_set_caps_from_attributes_simple_sdp:
* @ext: the #GstRTPHeaderExtension
* @caps: #GstCaps to write fields into
*
* Helper implementation for GstRTPExtensionClass::set_caps_from_attributes
* that sets the @ext uri on caps with the specified extension id as required
* for sdp #GstCaps.
*
* Requires that the extension does not have any attributes or direction
* advertised in @caps.
*
* Returns: whether the @ext attributes could be set on @caps.
*
* Since: 1.20
*/
gboolean
gst_rtp_header_extension_set_caps_from_attributes_simple_sdp
(GstRTPHeaderExtension * ext, GstCaps * caps) {
gchar *field_name = gst_rtp_header_extension_get_sdp_caps_field_name (ext);
GstStructure *s = gst_caps_get_structure (caps, 0);
gst_structure_set (s, field_name, G_TYPE_STRING,
gst_rtp_header_extension_get_uri (ext), NULL);
g_free (field_name);
return TRUE;
}
static gboolean
gst_rtp_ext_list_filter (GstPluginFeature * feature, gpointer user_data)
{
GstElementFactory *factory;
gchar *uri = user_data;
const gchar *klass, *factory_uri;
guint rank;
/* we only care about element factories */
if (!GST_IS_ELEMENT_FACTORY (feature))
return FALSE;
factory = GST_ELEMENT_FACTORY (feature);
/* only select elements with autoplugging rank */
rank = gst_plugin_feature_get_rank (feature);
if (rank < GST_RANK_MARGINAL)
return FALSE;
klass =
gst_element_factory_get_metadata (factory, GST_ELEMENT_METADATA_KLASS);
if (!strstr (klass, "Network") || !strstr (klass, "Extension") ||
!strstr (klass, "RTPHeader"))
return FALSE;
factory_uri =
gst_element_factory_get_metadata (factory,
GST_RTP_HEADER_EXTENSION_URI_METADATA_KEY);
if (!factory_uri)
return FALSE;
if (uri && g_strcmp0 (uri, factory_uri) != 0)
return FALSE;
return TRUE;
}
/**
* gst_rtp_get_header_extension_list:
*
* Retrieve all the factories of the currently registered RTP header
* extensions. Call gst_element_factory_create() with each factory to create
* the associated #GstRTPHeaderExtension.
*
* Returns: (transfer full) (element-type GstElementFactory): a #GList of
* #GstElementFactory's. Use gst_plugin_feature_list_free() after use
*
* Since: 1.20
*/
GList *
gst_rtp_get_header_extension_list (void)
{
return gst_registry_feature_filter (gst_registry_get (),
(GstPluginFeatureFilter) gst_rtp_ext_list_filter, FALSE, NULL);
}
/**
* gst_rtp_header_extension_create_from_uri:
* @uri: the rtp header extension URI to search for
*
* Returns: (transfer full) (nullable): the #GstRTPHeaderExtension for @uri or %NULL
*
* Since: 1.20
*/
GstRTPHeaderExtension *
gst_rtp_header_extension_create_from_uri (const gchar * uri)
{
GList *l;
l = gst_registry_feature_filter (gst_registry_get (),
(GstPluginFeatureFilter) gst_rtp_ext_list_filter, TRUE, (gpointer) uri);
if (l) {
GstElementFactory *factory = GST_ELEMENT_FACTORY (l->data);
GstElement *element = gst_element_factory_create (factory, NULL);
g_list_free_full (l, (GDestroyNotify) gst_object_unref);
return GST_RTP_HEADER_EXTENSION (element);
}
return NULL;
}