pad creation and some mistakes on gst_parse_launch - gstreamer

Question

I am a newbie to gstreamer and I would like to know if we have to create source and sink pads for convert like video convert in a pipeline. I have a pipeline like this
gst-launch-1.0 v4l2src ! video/x-raw,format=YUY2 ! videoconvert ! xvimagesink
I am trying to create a simple c application to understand the creation of pads and would like to know if video convert has a source pad and sink pad too. I am creating a source and sink pad for the filter.
EDIT:
yeah well you see, I tried following the dynamic pipelines example and wrote the code below
#include <gst/gst.h>
// easier to pass them as callbacks
typedef struct _CustomData{
GstElement *pipeline;
GstElement *source;
GstElement *convert;
GstElement *sink;
}CustomData;
// callback function
// here src is the v4l2src, newpad is gstpad that has just been added to src element. This is usually the pad to which we want to lnk
// data is the pointer we provided when attaching to the signal.
static void pad_added_handler(GstElement *src, GstPad *new_pad,CustomData *data)
{
g_print("In pad handler\n");
GstPad *sink_pad = gst_element_get_static_pad(data->convert, "sink");
GstPadLinkReturn ret;
GstCaps *new_pad_caps = NULL;
GstStructure *new_pad_struct = NULL;
const gchar *new_pad_type = NULL;
if(gst_pad_is_linked(sink_pad))
{
g_print("we are linked. igonring\n");
}
// check the new pad types
// we have previously created a piece of pipeline which deals with videoconvert linked with xvimagesink and we will nto be able to link it to a pad producing video.
//gst-pad_get_current_caps()- retrieves current capabilities of pad
new_pad_caps = gst_pad_get_current_caps(new_pad);
new_pad_struct = gst_caps_get_structure(new_pad_caps, 0);
new_pad_type = gst_structure_get_name(new_pad_struct);
g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);
if(!g_str_has_prefix(new_pad_type, "video/x-raw,format=(string)YUY2"))
{
g_print("It has new pad type");
}
// gst_pad_link tries to link two pads . the link must be specified from source to sink and both pads must be owned by elements residing in same pipeline
ret = gst_pad_link(new_pad, sink_pad);
if(GST_PAD_LINK_FAILED(ret))
{
g_print("type is new_pad_type");
}
if(new_pad_caps !=NULL)
{
gst_caps_unref(new_pad_caps);
}
gst_object_unref(sink_pad);
}
int main(int argc, char *argv[])
{
GMainLoop *loop;
CustomData data;
GstBus *bus;
GstMessage *msg;
gboolean terminate = FALSE;
gst_init(&argc, &argv);
// loop = g_main_loop_new(NULL, FALSE);
// create the elements
data.source = gst_element_factory_make("v4l2src", "source");
data.convert = gst_element_factory_make("videoconvert", "convert");
data.sink = gst_element_factory_make("xvimagesink", "sink");
data.pipeline = gst_pipeline_new("new-pipeline");
if(!data.pipeline || !data.source || !data.convert || !data.sink)
{
g_printerr("Not all elements could be created\n");
return -1;
}
//we did not link source at this point of time, we will do it later
gst_bin_add_many(GST_BIN(data.pipeline), data.source, data.convert, data.sink, NULL);
// we link convert element to sink, do not link them with source. we dont have source pads here. so we just have videoconvert->sink unlinked
// gst_element_link(data.source, data.convert);
if(!gst_element_link( data.convert,data.sink))
{
g_printerr("elements could not be linked\n");
gst_object_unref(data.pipeline);
return -1;
}
// we set the device source
//g_object_set(source, "device", "/dev/video0", NULL);
//connect to pad added signal.
// we want to attach pad added signal to source element. to do so, we are using g_signal_connect and provide callback function and datapointer.
// when source element has enough information to start producing data, it will create source pads and trigger the pad added signal. at this point, our callback is called
g_print("before signal connect\n");
gint id= g_signal_connect(G_OBJECT(data.source), "pad-added", G_CALLBACK(pad_added_handler), &data );
g_print("after signal connect with id = %d\n", id);
//g_signal_connect(G_OBJECT(data.source), "pad-added", G_CALLBACK(handler), &data);
// gst_element_link(data.source, data.convert);
GstStateChangeReturn ret;
ret =gst_element_set_state (data.pipeline, GST_STATE_PLAYING);
if (ret == GST_STATE_CHANGE_FAILURE) {
g_printerr ("Unable to set the pipeline to the playing state.\n");
gst_object_unref (data.pipeline);
return -1;
}
// g_main_loop_run(loop);
/* Listen to the bus */
bus = gst_element_get_bus (data.pipeline);
do {
msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
/* Parse message */
if (msg != NULL) {
GError *err;
gchar *debug_info;
switch (GST_MESSAGE_TYPE (msg)) {
case GST_MESSAGE_ERROR:
gst_message_parse_error (msg, &err, &debug_info);
g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");
g_clear_error (&err);
g_free (debug_info);
terminate = TRUE;
break;
case GST_MESSAGE_EOS:
g_print ("End-Of-Stream reached.\n");
terminate = TRUE;
break;
case GST_MESSAGE_STATE_CHANGED:
/* We are only interested in state-changed messages from the pipeline */
if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)) {
GstState old_state, new_state, pending_state;
gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);
g_print ("Pipeline state changed from %s to %s:\n",
gst_element_state_get_name (old_state), gst_element_state_get_name (new_state));
}
break;
default:
/* We should not reach here */
g_printerr ("Unexpected message received.\n");
break;
}
gst_message_unref (msg);
}
} while (!terminate);
/* Free resources */
gst_object_unref (bus);
gst_element_set_state(data.pipeline, GST_STATE_NULL);
gst_object_unref(data.pipeline);
return 0;
}
and it gave me an error
before signal connect
after signal connect with id = 1
Pipeline state changed from NULL to READY:
Pipeline state changed from READY to PAUSED:
Error received from element source: Internal data stream error.
Debugging information: gstbasesrc.c(3055): gst_base_src_loop (): /GstPipeline:new-pipeline/GstV4l2Src:source:
streaming stopped, reason not-linked (-1)
(The above code works if I write gst_elements_link(data.source, data.convert) after the element link statement for convert and sink)
So I tried the normal way in which I just added and linked all the elements together and it began to work without use of the pads.
#include <gst/gst.h>
int main(int argc, char *argv[])
{
GstElement *pipeline, *source, *convert, *sink;
GstBus *bus;
GstMessage *msg;
gst_init(&argc, &argv);
source = gst_element_factory_make("v4l2src", "source");
convert = gst_element_factory_make("nvvidconv", "convert");
sink = gst_element_factory_make("xvimagesink", "sink");
pipeline = gst_pipeline_new("pipe");
gst_bin_add_many(GST_BIN(pipeline), source,convert,sink, NULL);
gst_element_link_many(source,convert,sink,NULL);
gst_element_set_state(pipeline,GST_STATE_PLAYING);
bus = gst_element_get_bus (pipeline);
msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE, GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
/* Parse message */
if (msg != NULL) {
GError *err;
gchar *debug_info;
switch (GST_MESSAGE_TYPE (msg)) {
case GST_MESSAGE_ERROR:
gst_message_parse_error (msg, &err, &debug_info);
g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");
g_clear_error (&err);
g_free (debug_info);
break;
case GST_MESSAGE_EOS:
g_print ("End-Of-Stream reached.\n");
break;
default:
/* We should not reach here because we only asked for ERRORs and EOS */
g_printerr ("Unexpected message received.\n");
break;
}
gst_message_unref (msg);
}
/* Free resources */
gst_object_unref(bus);
gst_element_set_state(pipeline,GST_STATE_NULL);
gst_object_unref(pipeline);
}
But, inorder to fully grasp the knowledge of pads, I wanted to execute simpler pipelines with pads.
I just don't fully understand the usage of pads and link them and all.
EDIT2:
Ultimately I want to write application for pipeline like this which works on command line perfectly well,
gst-launch-1.0 v4l2src device='/dev/video0' ! 'video/x-raw,format=(string)YUY2,width=(int)640,height=(int)480' ! nvvidconv ! 'video/x-raw(memory:NVMM),format=(string)NV12,width=(int)640,height=(int)480' ! nvvidconv ! 'video/x-raw,format=(string)NV12,width=(int)640,height=(int)480' ! nvvideoconvert ! 'video/x-raw(memory:NVMM),format=(string)NV12,width=(int)640,height=(int)480' ! mux.sink_0 nvstreammux live-source=1 name=mux batch-size=1 width=640 height=480 ! nvinfer config-file-path=/opt/nvidia/deepstream/deepstream-4.0/sources/apps/sample_apps/deepstream-test1/dstest1_pgie_config.txt batch-size=1 ! nvmultistreamtiler rows=1 columns=1 width=640 height=480 ! nvvideoconvert ! nvdsosd ! nvegltransform ! nveglglessink sync=false -v
But as I don't understand the usage of both pads and bins, I am unable to implement them in my above pipeline. However, I tried this,
#include <gst/gst.h>
#include <glib.h>
#include <stdio.h>
#include "gstnvdsmeta.h"
#define MAX_DISPLAY_LEN 64
#define PGIE_CLASS_ID_VEHICLE 0
#define PGIE_CLASS_ID_PERSON 2
gint frame_number = 0;
gchar pgie_classes_str[4][32] = { "Vehicle", "TwoWheeler", "Person",
"Roadsign"
};
static GstPadProbeReturn osd_sink_pad_buffer_probe(GstPad *pad, GstPadProbeInfo *info, gpointer u_data)
{
GstBuffer *buf=(GstBuffer *)info->data;
guint num_rects =0;
NvDsObjectMeta *obj_meta = NULL;
guint vehicle_count = 0;
guint person_count = 0;
NvDsMetaList * l_frame = NULL;
NvDsMetaList * l_obj = NULL;
NvDsDisplayMeta *display_meta = NULL;
NvDsBatchMeta *batch_meta = gst_buffer_get_nvds_batch_meta (buf);
for (l_frame = batch_meta->frame_meta_list; l_frame != NULL;
l_frame = l_frame->next) {
NvDsFrameMeta *frame_meta = (NvDsFrameMeta *) (l_frame->data);
int offset = 0;
for (l_obj = frame_meta->obj_meta_list; l_obj != NULL;
l_obj = l_obj->next) {
obj_meta = (NvDsObjectMeta *) (l_obj->data);
if (obj_meta->class_id == PGIE_CLASS_ID_VEHICLE) {
vehicle_count++;
num_rects++;
}
if (obj_meta->class_id == PGIE_CLASS_ID_PERSON) {
person_count++;
num_rects++;
}
}
display_meta = nvds_acquire_display_meta_from_pool(batch_meta);
NvOSD_TextParams *txt_params = &display_meta->text_params[0];
display_meta->num_labels = 1;
txt_params->display_text = g_malloc0 (MAX_DISPLAY_LEN);
offset = snprintf(txt_params->display_text, MAX_DISPLAY_LEN, "Person = %d ", person_count);
offset = snprintf(txt_params->display_text + offset , MAX_DISPLAY_LEN, "Vehicle = %d ", vehicle_count);
/* Now set the offsets where the string should appear */
txt_params->x_offset = 10;
txt_params->y_offset = 12;
/* Font , font-color and font-size */
txt_params->font_params.font_name = "Serif";
txt_params->font_params.font_size = 10;
txt_params->font_params.font_color.red = 1.0;
txt_params->font_params.font_color.green = 1.0;
txt_params->font_params.font_color.blue = 1.0;
txt_params->font_params.font_color.alpha = 1.0;
/* Text background color */
txt_params->set_bg_clr = 1;
txt_params->text_bg_clr.red = 0.0;
txt_params->text_bg_clr.green = 0.0;
txt_params->text_bg_clr.blue = 0.0;
txt_params->text_bg_clr.alpha = 1.0;
nvds_add_display_meta_to_frame(frame_meta, display_meta);
}
g_print ("Frame Number = %d Number of objects = %d "
"Vehicle Count = %d Person Count = %d\n",
frame_number, num_rects, vehicle_count, person_count);
frame_number++;
return GST_PAD_PROBE_OK;
}
int main(int argc, char *argv[])
{
GstElement *pipeline, *source, *filter1, *convert,*filter2, *filter3, *vidconv, *filter4, *mux, *infer, *tiler, *osd, *transform , *sink, *bin, *convert2 , *vidconv2;
GMainLoop *loop;
GstCaps *caps1, *caps2, *caps3, *caps4;
GstPad *osd_sink_pad =NULL, *srcpad, *sinkpad;
loop = g_main_loop_new(NULL,FALSE);
gst_init(&argc, &argv);
pipeline = gst_pipeline_new("nv_pipeline");
gchar *string1 = "video/x-raw(memory:NVMM),format=(string)NV12";
source = gst_element_factory_make("v4l2src", "source");
filter1 = gst_element_factory_make("capsfilter", "filter1");
convert = gst_element_factory_make("nvvidconv", "convert");
filter2 = gst_element_factory_make("capsfilter", "filter2");
filter3 = gst_element_factory_make("capsfilter", "filter3");
filter4 = gst_element_factory_make("capsfilter", "filter4");
vidconv = gst_element_factory_make("nvvideoconvert", "vidconv");
mux = gst_element_factory_make("nvstreammux", "mux");
infer = gst_element_factory_make("nvinfer", "infer");
tiler = gst_element_factory_make("nvmultistreamtiler", "tiler");
osd = gst_element_factory_make("nvosd", "osd");
transform = gst_element_factory_make("nvegltransform", "transform");
sink = gst_element_factory_make("nveglglessink", "sink");
convert2 = gst_element_factory_make("nvvidconv", "convert2");
vidconv2 = gst_element_factory_make("nvvideoconvert", "vidconv2");
gst_bin_add_many(GST_BIN(pipeline), source,filter1,convert,filter2, convert2,filter3,vidconv, filter4,mux,infer, tiler,vidconv2, osd,transform,sink,NULL);
gst_element_link_many(source,filter1,convert,filter2, convert2,filter3, vidconv, filter4,mux,infer, tiler,vidconv2, osd,transform,sink,NULL);
osd_sink_pad = gst_element_get_static_pad(osd, "sink");
gst_pad_add_probe(osd_sink_pad, GST_PAD_PROBE_TYPE_BUFFER, osd_sink_pad_buffer_probe, NULL, NULL);
caps1 = gst_caps_new_simple("video/x-raw", "format",G_TYPE_STRING,"YUY2",NULL);
caps2 = gst_caps_from_string(string1);
caps3 = gst_caps_new_simple("video/x-raw", "format", G_TYPE_STRING,"NV12", NULL);
caps4 = gst_caps_from_string(string1);
g_object_set(G_OBJECT(filter1), "caps", caps1, NULL);
g_object_set(G_OBJECT(filter2), "caps", caps2, NULL);
g_object_set(G_OBJECT(filter3), "caps", caps3, NULL);
g_object_set(G_OBJECT(filter4), "caps", caps4, NULL);
g_object_set(G_OBJECT(mux), "live-source", 1, "name", "mux", "batch-size", 1, "width", 1280, "height", 720, NULL);
g_object_set(G_OBJECT(infer), "config-file-path","/opt/nvidia/deepstream/deepstream-4.0/sources/apps/sample_apps/deepstream-test1/dstest1_pgie_config.txt",NULL);
g_object_set(G_OBJECT(infer), "batch-size", 1, NULL);
g_object_set(G_OBJECT(tiler), "rows", 1, "columns", 1, "width", 1280, "height", 720, NULL);
gst_caps_unref(caps1);
gst_caps_unref(caps2);
gst_caps_unref(caps3);
gst_caps_unref(caps4);
gst_element_set_state(pipeline, GST_STATE_PLAYING);
g_print("Running ...\n");
g_main_loop_run(loop);
gst_element_set_state(pipeline,GST_STATE_NULL);
gst_object_unref(pipeline);
return 0;
}
which gives the exact same output as the command line gst-launch-1.0 like,
(deep_pads:15648): GLib-GObject-WARNING **: 11:29:18.761: cannot register existing type 'GstInterpolationMethod'
(deep_pads:15648): GLib-GObject-CRITICAL **: 11:29:18.761: g_param_spec_enum: assertion 'G_TYPE_IS_ENUM (enum_type)' failed
(deep_pads:15648): GLib-GObject-CRITICAL **: 11:29:18.761: validate_pspec_to_install: assertion 'G_IS_PARAM_SPEC (pspec)' failed
(deep_pads:15648): GStreamer-CRITICAL **: 11:29:18.814: gst_element_get_static_pad: assertion 'GST_IS_ELEMENT (element)' failed
(deep_pads:15648): GStreamer-CRITICAL **: 11:29:18.814: gst_pad_add_probe: assertion 'GST_IS_PAD (pad)' failed
0:00:00.843318172 15648 0x5591be52c0 INFO nvinfer gstnvinfer.cpp:519:gst_nvinfer_logger:<infer> NvDsInferContext[UID 1]:initialize(): Trying to create engine from model files
0:00:20.693301580 15648 0x5591be52c0 INFO nvinfer gstnvinfer.cpp:519:gst_nvinfer_logger:<infer> NvDsInferContext[UID 1]:generateTRTModel(): Storing the serialized cuda engine to file at /opt/nvidia/deepstream/deepstream-4.0/samples/models/Primary_Detector/resnet10.caffemodel_b1_int8.engine
except It doesn't display an output window from the above c application and doesn't display the rest.

Answer 1

Your first example fails because data.source element is actually never linked to data.convert element. Since both elements have static pads you need to "manually" create them and link them before setting pipeline to GST_STATE_PLAYING:
GstPad *source_pad = gst_element_get_static_pad(data.source, "src");
GstPad *sink_pad = gst_element_get_static_pad(data.convert, "sink");
ret = gst_pad_link(source_pad, sink_pad);
You probably expected that static source pad of your data.source element will somehow be automatically created so you registered
g_signal_connect(G_OBJECT(data.source), "pad-added", G_CALLBACK(pad_added_handler), &data );
But, as you can see from your debug, pad_added_handler was never called because g_signal_connect can be registered and will be called for elements that have dynamic pads. For example, demultiplexer tsdemux will dynamically create its source pads during discovery of elementary streams so, in that case, registration of pad-added callback would be necessary.
The first step in your learning curve would be to understand fundamental differences between "static" (mandatory, always exists, "manually" created), dynamic (exists sometimes, automatically created by element) and request (optional, "manually" created when needed) gstreamer pads. After that everything will be much easier for you.