The UDPSRC GStreamer plugin is a source element that receives UDP packets from a port and provides them to the GStreamer pipeline. It has properties to configure the port, multicast group, interface, URI, buffer size, and other settings. The init functions initialize the element and register its properties. The main functions open the socket, start/stop listening, handle incoming packets, and provide data to the pipeline in response to requests.

1. UDPSRC Gstreamer Plugin
Session VIII

2. UDPSRC - Overview
• Source element
– Receives the packet from UDP port & provide it
over gstreamer pipeline
– Contains Single PAD ( source PAD )

3. Properties
• PROP_PORT
• PROP_MULTICAST_GROUP
• PROP_MULTICAST_IFACE
• PROP_URI
• PROP_CAPS
• PROP_SOCKFD
• PROP_BUFFER_SIZE
• PROP_TIMEOUT
• PROP_SKIP_FIRST_BYTES
• PROP_CLOSEFD
• PROP_SOCK
• PROP_AUTO_MULTICAST
• PROP_REUSE

4. gst_udpsrc_base_init
• Does the base initialization of udpsrc source
element
• Adds / registers the static source PAD

5. gst_udpsrc_base_init
static void gst_udpsrc_base_init (gpointer g_class)
{
GstElementClass *element_class = GST_ELEMENT_CLASS (g_class);
gst_element_class_add_static_pad_template (element_class,
&src_template);
gst_element_class_set_details_simple (element_class, "UDP packet
receiver",
"Source/Network",
"Receive data over the network via UDP",
"Wim Taymans <wim@fluendo.com>, "
"Thijs Vermeir <thijs.vermeir@barco.com>");
}

6. gst_udpsrc_class_init
• Call back function initialization to
– Get property - gst_udpsrc_get_property
– Set property - gst_udpsrc_set_property
– Finalize - gst_udpsrc_finalize
– Start - gst_udpsrc_start
– Stop - gst_udpsrc_stop
– Unlock - gst_udpsrc_unlock
– Unlock_stop - gst_udpsrc_unlock_stop
– Getcaps - gst_udpsrc_getcaps
– Create - gst_udpsrc_create

7. gst_udpsrc_class_init
• Initialization / registeration of element properties
– Port – Port Number ( int )
– Multicast-group : Name of group ( String )
– Multicast-iface : Name of Interface ( String )
– Uri : string
– Sockfd – Socket handler ( int )
– Buffer-size – Buffer-Size (int )
– Timeout – (int)
– Skip First bytes – Number of byte to skip ( int )
– closeFd – Close sockfd if passed as property of state change ( int )
– Sock – Socket Handle ( int )
– Auto-multicast – Automatically joins / leaves multicast groups ( int )
– Reuse : Enables reuse of the port ( boolean )

8. Property registration
• Property registration is done by
– g_object_class_install_property
• Parameter specified by either
– g_param_spec_int
– g_param_spec_string
– g_param_spec_boolean
– g_param_spec_uint64

9. gst_udpsrc_init
• Initializes uri string
• Initializes all the property variables

10. gst_udpsrc_finalize
• This does the cleanup & frees the memory
• unref the capabilities
• frees memory of multicast_iface
• frees memory of uri & uristr
• Closes the socket, if closeFd option enabled
• Cleanup the object
• Finalize gstreamer base object

11. gst_udpsrc_getcaps
static GstCaps *
gst_udpsrc_getcaps (GstBaseSrc * src)
{
GstUDPSrc *udpsrc;
udpsrc = GST_UDPSRC (src);
if (udpsrc->caps)
return gst_caps_ref (udpsrc->caps);
else
return gst_caps_new_any ();
}

12. clear_error
• Reads a message from error queue
• Flushes ERROR from fd so next poll will not
return at once
• Local address handling without address

13. gst_udpsrc_start
• Gets URI information
• Creates a socket
• Enables port reuse option using setsockopt, if
reuse is enabled
• Set socket name if it is multicast
• Configure the kernel receiver buffer size, if buffer-
size parameter is given
• Add the socket into poll fd
• Add the socket into control fd read

14. gst_udpsrc_stop
static gboolean
gst_udpsrc_stop (GstBaseSrc * bsrc)
{
GstUDPSrc *src;
src = GST_UDPSRC (bsrc);
GST_DEBUG ("stopping, closing sockets");
if (src->sock.fd >= 0) {
if (src->auto_multicast && gst_udp_is_multicast (&src->myaddr)) {
GST_DEBUG_OBJECT (src, "leaving multicast group %s", src->uri.host);
gst_udp_leave_group (src->sock.fd, &src->myaddr);
}
CLOSE_IF_REQUESTED (src);
}
if (src->fdset) {
gst_poll_free (src->fdset);
src->fdset = NULL;
}
return TRUE;
}

15. gst_udpsrc_create
• Wait for the socket data using gst_poll_wait
• Recv the packet from socket using recvfrom
• Allocate memory for sending data to stream
• Skip first bytes if the option is enabled
• Buffer cast the data to flow into pipeline.

16. Get Type & Protocols
static GstURIType
gst_udpsrc_uri_get_type (void)
{
return GST_URI_SRC;
}
static gchar **
gst_udpsrc_uri_get_protocols (void)
{
static gchar *protocols[] = { (char *) "udp", NULL };
return protocols;
}

17. Get & Set URI
static const gchar * gst_udpsrc_uri_get_uri (GstURIHandler * handler)
{
GstUDPSrc *src = GST_UDPSRC (handler);
g_free (src->uristr);
src->uristr = gst_udp_uri_string (&src->uri);
return src->uristr;
}
static gboolean gst_udpsrc_uri_set_uri (GstURIHandler * handler, const gchar * uri)
{
gboolean ret;
GstUDPSrc *src = GST_UDPSRC (handler);
ret = gst_udpsrc_set_uri (src, uri);
return ret;
}

18. gst_udpsrc_uri_handler_init
static void
gst_udpsrc_uri_handler_init (gpointer g_iface, gpointer
iface_data)
{
GstURIHandlerInterface *iface = (GstURIHandlerInterface *)
g_iface;
iface->get_type = gst_udpsrc_uri_get_type;
iface->get_protocols = gst_udpsrc_uri_get_protocols;
iface->get_uri = gst_udpsrc_uri_get_uri;
iface->set_uri = gst_udpsrc_uri_set_uri;
}