Python to C code

Hi,
i’m trying to rewrite deepstream_test_1_usb.py in c.

I’m having trouble setting the properties of “caps”. specifically, these two lines:

caps_v4l2src.set_property(‘caps’, Gst.Caps.from_string(“video/x-raw, framerate=30/1”))
caps_vidconvsrc.set_property(‘caps’, Gst.Caps.from_string(“video/x-raw(memory:NVMM)”))

how can i translate them into c?

I am also attaching the complete code of the app

*#!/usr/bin/env python3

################################################################################

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################################################################################

import sys
sys.path.append(’…/’)
import gi
gi.require_version(‘Gst’, ‘1.0’)
from gi.repository import GObject, Gst
from common.is_aarch_64 import is_aarch64
from common.bus_call import bus_call

import pyds

PGIE_CLASS_ID_VEHICLE = 0
PGIE_CLASS_ID_BICYCLE = 1
PGIE_CLASS_ID_PERSON = 2
PGIE_CLASS_ID_ROADSIGN = 3

def osd_sink_pad_buffer_probe(pad,info,u_data):
frame_number=0
#Intiallizing object counter with 0.
obj_counter = {
PGIE_CLASS_ID_VEHICLE:0,
PGIE_CLASS_ID_PERSON:0,
PGIE_CLASS_ID_BICYCLE:0,
PGIE_CLASS_ID_ROADSIGN:0
}
num_rects=0

gst_buffer = info.get_buffer()
if not gst_buffer:
    print("Unable to get GstBuffer ")
    return

# Retrieve batch metadata from the gst_buffer
# Note that pyds.gst_buffer_get_nvds_batch_meta() expects the
# C address of gst_buffer as input, which is obtained with hash(gst_buffer)
batch_meta = pyds.gst_buffer_get_nvds_batch_meta(hash(gst_buffer))
l_frame = batch_meta.frame_meta_list
while l_frame is not None:
    try:
        # Note that l_frame.data needs a cast to pyds.NvDsFrameMeta
        # The casting is done by pyds.NvDsFrameMeta.cast()
        # The casting also keeps ownership of the underlying memory
        # in the C code, so the Python garbage collector will leave
        # it alone.
       frame_meta = pyds.NvDsFrameMeta.cast(l_frame.data)
    except StopIteration:
        break

    frame_number=frame_meta.frame_num
    num_rects = frame_meta.num_obj_meta
    l_obj=frame_meta.obj_meta_list
    while l_obj is not None:
        try:
            # Casting l_obj.data to pyds.NvDsObjectMeta
            obj_meta=pyds.NvDsObjectMeta.cast(l_obj.data)
        except StopIteration:
            break
        obj_counter[obj_meta.class_id] += 1
        try: 
            l_obj=l_obj.next
        except StopIteration:
            break

    # Acquiring a display meta object. The memory ownership remains in
    # the C code so downstream plugins can still access it. Otherwise
    # the garbage collector will claim it when this probe function exits.
    display_meta=pyds.nvds_acquire_display_meta_from_pool(batch_meta)
    display_meta.num_labels = 1
    py_nvosd_text_params = display_meta.text_params[0]
    # Setting display text to be shown on screen
    # Note that the pyds module allocates a buffer for the string, and the
    # memory will not be claimed by the garbage collector.
    # Reading the display_text field here will return the C address of the
    # allocated string. Use pyds.get_string() to get the string content.
    py_nvosd_text_params.display_text = "Frame Number={} Number of Objects={} Vehicle_count={} Person_count={}".format(frame_number, num_rects, obj_counter[PGIE_CLASS_ID_VEHICLE], obj_counter[PGIE_CLASS_ID_PERSON])

    # Now set the offsets where the string should appear
    py_nvosd_text_params.x_offset = 10
    py_nvosd_text_params.y_offset = 12

    # Font , font-color and font-size
    py_nvosd_text_params.font_params.font_name = "Serif"
    py_nvosd_text_params.font_params.font_size = 10
    # set(red, green, blue, alpha); set to White
    py_nvosd_text_params.font_params.font_color.set(1.0, 1.0, 1.0, 1.0)

    # Text background color
    py_nvosd_text_params.set_bg_clr = 1
    # set(red, green, blue, alpha); set to Black
    py_nvosd_text_params.text_bg_clr.set(0.0, 0.0, 0.0, 1.0)
    # Using pyds.get_string() to get display_text as string
    print(pyds.get_string(py_nvosd_text_params.display_text))
    pyds.nvds_add_display_meta_to_frame(frame_meta, display_meta)
    try:
        l_frame=l_frame.next
    except StopIteration:
        break
		
return Gst.PadProbeReturn.OK	

def main(args):
# Check input arguments
if len(args) != 2:
sys.stderr.write(“usage: %s \n” % args[0])
sys.exit(1)

# Standard GStreamer initialization
GObject.threads_init()
Gst.init(None)

# Create gstreamer elements
# Create Pipeline element that will form a connection of other elements
print("Creating Pipeline \n ")
pipeline = Gst.Pipeline()

if not pipeline:
    sys.stderr.write(" Unable to create Pipeline \n")

# Source element for reading from the file
print("Creating Source \n ")
source = Gst.ElementFactory.make("v4l2src", "usb-cam-source")
if not source:
    sys.stderr.write(" Unable to create Source \n")

caps_v4l2src = Gst.ElementFactory.make("capsfilter", "v4l2src_caps")
if not caps_v4l2src:
    sys.stderr.write(" Unable to create v4l2src capsfilter \n")


print("Creating Video Converter \n")

# Adding videoconvert -> nvvideoconvert as not all
# raw formats are supported by nvvideoconvert;
# Say YUYV is unsupported - which is the common
# raw format for many logi usb cams
# In case we have a camera with raw format supported in
# nvvideoconvert, GStreamer plugins' capability negotiation
# shall be intelligent enough to reduce compute by
# videoconvert doing passthrough (TODO we need to confirm this)


# videoconvert to make sure a superset of raw formats are supported
vidconvsrc = Gst.ElementFactory.make("videoconvert", "convertor_src1")
if not vidconvsrc:
    sys.stderr.write(" Unable to create videoconvert \n")

# nvvideoconvert to convert incoming raw buffers to NVMM Mem (NvBufSurface API)
nvvidconvsrc = Gst.ElementFactory.make("nvvideoconvert", "convertor_src2")
if not nvvidconvsrc:
    sys.stderr.write(" Unable to create Nvvideoconvert \n")

caps_vidconvsrc = Gst.ElementFactory.make("capsfilter", "nvmm_caps")
if not caps_vidconvsrc:
    sys.stderr.write(" Unable to create capsfilter \n")

# Create nvstreammux instance to form batches from one or more sources.
streammux = Gst.ElementFactory.make("nvstreammux", "Stream-muxer")
if not streammux:
    sys.stderr.write(" Unable to create NvStreamMux \n")

# Use nvinfer to run inferencing on camera's output,
# behaviour of inferencing is set through config file
pgie = Gst.ElementFactory.make("nvinfer", "primary-inference")
if not pgie:
    sys.stderr.write(" Unable to create pgie \n")

# Use convertor to convert from NV12 to RGBA as required by nvosd
nvvidconv = Gst.ElementFactory.make("nvvideoconvert", "convertor")
if not nvvidconv:
    sys.stderr.write(" Unable to create nvvidconv \n")

# Create OSD to draw on the converted RGBA buffer
nvosd = Gst.ElementFactory.make("nvdsosd", "onscreendisplay")

if not nvosd:
    sys.stderr.write(" Unable to create nvosd \n")

# Finally render the osd output
if is_aarch64():
    transform = Gst.ElementFactory.make("nvegltransform", "nvegl-transform")

print("Creating EGLSink \n")
sink = Gst.ElementFactory.make("nveglglessink", "nvvideo-renderer")
if not sink:
    sys.stderr.write(" Unable to create egl sink \n")

print("Playing cam %s " %args[1])
caps_v4l2src.set_property('caps', Gst.Caps.from_string("video/x-raw, framerate=30/1"))
caps_vidconvsrc.set_property('caps', Gst.Caps.from_string("video/x-raw(memory:NVMM)"))
source.set_property('device', args[1])
streammux.set_property('width', 1920)
streammux.set_property('height', 1080)
streammux.set_property('batch-size', 1)
streammux.set_property('batched-push-timeout', 4000000)
pgie.set_property('config-file-path', "dstest1_pgie_config.txt")
# Set sync = false to avoid late frame drops at the display-sink
sink.set_property('sync', False)

print("Adding elements to Pipeline \n")
pipeline.add(source)
pipeline.add(caps_v4l2src)
pipeline.add(vidconvsrc)
pipeline.add(nvvidconvsrc)
pipeline.add(caps_vidconvsrc)
pipeline.add(streammux)
pipeline.add(pgie)
pipeline.add(nvvidconv)
pipeline.add(nvosd)
pipeline.add(sink)
if is_aarch64():
    pipeline.add(transform)

# we link the elements together
# v4l2src -> nvvideoconvert -> mux -> 
# nvinfer -> nvvideoconvert -> nvosd -> video-renderer
print("Linking elements in the Pipeline \n")
source.link(caps_v4l2src)
caps_v4l2src.link(vidconvsrc)
vidconvsrc.link(nvvidconvsrc)
nvvidconvsrc.link(caps_vidconvsrc)

sinkpad = streammux.get_request_pad("sink_0")
if not sinkpad:
    sys.stderr.write(" Unable to get the sink pad of streammux \n")
srcpad = caps_vidconvsrc.get_static_pad("src")
if not srcpad:
    sys.stderr.write(" Unable to get source pad of caps_vidconvsrc \n")
srcpad.link(sinkpad)
streammux.link(pgie)
pgie.link(nvvidconv)
nvvidconv.link(nvosd)
if is_aarch64():
    nvosd.link(transform)
    transform.link(sink)
else:
    nvosd.link(sink)

# create an event loop and feed gstreamer bus mesages to it
loop = GObject.MainLoop()
bus = pipeline.get_bus()
bus.add_signal_watch()
bus.connect ("message", bus_call, loop)

# Lets add probe to get informed of the meta data generated, we add probe to
# the sink pad of the osd element, since by that time, the buffer would have
# had got all the metadata.
osdsinkpad = nvosd.get_static_pad("sink")
if not osdsinkpad:
    sys.stderr.write(" Unable to get sink pad of nvosd \n")

osdsinkpad.add_probe(Gst.PadProbeType.BUFFER, osd_sink_pad_buffer_probe, 0)

# start play back and listen to events
print("Starting pipeline \n")
pipeline.set_state(Gst.State.PLAYING)
try:
    loop.run()
except:
    pass
# cleanup
pipeline.set_state(Gst.State.NULL)

if name == ‘main’:
sys.exit(main(sys.argv))
*

Are you familiar with our DeepStream C/C++ sample codes? You can refer to the C/C++ codes directly. You can find the source codes in /opt/nvidia/deepstream/deepstream-5.0/sources/ folder in your Nvidia device.

Python DeepStream is based on gstreamer python(https://gstreamer.freedesktop.org/modules/gst-python.html) and Nvidia DeepStream pyds(), it is necessary to learn DeepStream C/C++ before starting to learn and use DeepStream python.

GStreamer python reference:
https://lazka.github.io/pgi-docs/
DeepStream pyds reference:
https://docs.nvidia.com/metropolis/deepstream/python-api/
GStreamer C APIs:
https://gstreamer.freedesktop.org/documentation/libs.html?gi-language=c
Glib core APIs:
https://developer.gnome.org/glib/2.64/glib-core.html