GStreamer bitrate does not work the same when implemented in C++ compared to command line get-launch-1.0 (x264enc & omxh264enc) - c++

Question

I encountered different behavior with a gstreamer pipelines when implemented in C++ compared to gst-launch-1.0 execution in command line - the problem is with the bitrate property.
Same problem as described bellow in both implementations (C++ & command line execution) occurs with omxh264enc encoder as well with control-rate property set to 2 (CBR mode).
The pipeline which used in command line was:
gst-launch-1.0 ximagesrc ! autovideoconvert ! x264enc bitrate=800 pass=0 ! video/x-h264, stream-format=byte-stream ! h264parse ! mpegtsmux ! udpsink host=127.0.0.1 port=1234 sync=false
The C++ implementation is:
GstElement* pipeline;
GstElement* appsrc;
GstElement* videoConvert;
GstElement* encoder;
GstElement* encoderCapsFilter;
GstElement* parser;
GstElement* tsmux;
GstElement* udpsink;
pipeline = gst_pipeline_new ("pipeline");
appsrc = gst_element_factory_make ("appsrc", "source");
videoConvert = gst_element_factory_make ("autovideoconvert", "my_video_convertor");
encoder = gst_element_factory_make ("x264enc", "my_encoder");
encoderCapsFilter = gst_element_factory_make("capsfilter", "my_caps");
parser = gst_element_factory_make ("h264parse", "my_parser");
tsmux = gst_element_factory_make ("mpegtsmux", "my_muxer");
udpsink = gst_element_factory_make ("udpsink", "my_udpsink");
/*Configure appsrc*/
g_object_set (G_OBJECT (appsrc), "caps", gst_caps_new_simple ("video/x-raw",
"format", G_TYPE_STRING, "I420",
"width", G_TYPE_INT, width,
"height", G_TYPE_INT, height,
"framerate", GST_TYPE_FRACTION, 25, 1, NULL), NULL);
g_object_set(G_OBJECT(appsrc), "is-live" , true, NULL);
/*Configure videoConvert*/
/*Configure encoder*/
g_object_set(G_OBJECT(encoder), "bitrate" , 800, NULL);
g_object_set(G_OBJECT(encoder), "pass" , 0, NULL);
/*Configure encoder caps*/
g_object_set(G_OBJECT (encoderCapsFilter), "caps", gst_caps_from_string("video/x-h264, stream-format=byte-stream"), NULL);
/*Configure h264parse*/
/*Configure mpegtsmux*/
/*Configure udpsink*/
g_object_set(G_OBJECT(udpsink), "host" , "127.0.0.1", NULL);
g_object_set(G_OBJECT(udpsink), "port" , 1234, NULL);
g_object_set(G_OBJECT(udpsink), "sync" , false, NULL);
// add
gst_bin_add_many(GST_BIN(pipeline),
appsrc,
videoConvert,
encoder,
encoderCapsFilter,
parser,
tsmux,
udpsink,
NULL);
// link
if (!gst_element_link_many(appsrc,
videoConvert,
encoder,
encoderCapsFilter,
parser,
tsmux,
udpsink,
NULL))
{
g_printerr("Elements could not be linked");
}
bitrate is set to 800kbps and when testing this pipeline from command line with Wireshark the baudrate results around 800-850kbps which is good,
when tested the same pipeline in C++ (to use appsrc instead of ximagesrc) the baudrate results in different and higher bitrate (around 1200-1300kbps).
What is missing to reach the same bitrate result when executed through command line?
Is there more configuration to be done into the gst elements when implemented in C++?