“Request” pads are similar to sometimes pads, except that
request are created on demand of something outside of the element rather
than something inside the element. This concept is often used in muxers,
where - for each elementary stream that is to be placed in the output
system stream - one sink pad will be requested. It can also be used in
elements with a variable number of input or outputs pads, such as the
tee
(multi-output) or
input-selector
(multi-input) elements.
To implement request pads, you need to provide a padtemplate with a
GST_PAD_REQUEST presence and implement the
request_new_pad
virtual method in
GstElement
.
To clean up, you will need to implement the
release_pad
virtual method.
static GstPad * gst_my_filter_request_new_pad (GstElement *element, GstPadTemplate *templ, const gchar *name, const GstCaps *caps); static void gst_my_filter_release_pad (GstElement *element, GstPad *pad); static GstStaticPadTemplate sink_factory = GST_STATIC_PAD_TEMPLATE ( "sink_%u", GST_PAD_SINK, GST_PAD_REQUEST, GST_STATIC_CAPS ("ANY") ); static void gst_my_filter_class_init (GstMyFilterClass *klass) { GstElementClass *element_class = GST_ELEMENT_CLASS (klass); [..] gst_element_class_add_pad_template (klass, gst_static_pad_template_get (&sink_factory)); [..] element_class->request_new_pad = gst_my_filter_request_new_pad; element_class->release_pad = gst_my_filter_release_pad; } static GstPad * gst_my_filter_request_new_pad (GstElement *element, GstPadTemplate *templ, const gchar *name, const GstCaps *caps) { GstPad *pad; GstMyFilterInputContext *context; context = g_new0 (GstMyFilterInputContext, 1); pad = gst_pad_new_from_template (templ, name); gst_pad_set_element_private (pad, context); /* normally, you would set _chain () and _event () functions here */ gst_element_add_pad (element, pad); return pad; } static void gst_my_filter_release_pad (GstElement *element, GstPad *pad) { GstMyFilterInputContext *context; context = gst_pad_get_element_private (pad); g_free (context); gst_element_remove_pad (element, pad); }