Strange delay in video streaming after short-cutting pipeline | Appsink-Appsrc | H.265 byte stream

[jeyp4]

Hello

In a C++ development, I divide a pipeline with help of appsink-appsrc.
v4l2src device=/dev/video0 !
'video/x-raw,format=(string)YV12,width=1280,height=720,framerate=(fraction)25/1'
! vaapih265enc ! appsink
&
appsrc ! vaapidecode ! xvimagesink


Problem : I am facing an expected delay in video-steaming of around ~500ms.
I am sure that this delay is not due to data-transmission. Because both
application runs on same PC. To confirm this, I time-stamped the h.265 bytes
and calculated data-transmission delay (~1ms).

I am doubting that, I have to tweak appsink-appsrc elements. May be changing
their properties.

My code snippets look like

*Appsink*
_sink = gst_element_factory_make("appsink", "sink");
g_object_set(_sink, "emit-signals", TRUE, "max-buffers", 1, "drop", TRUE,
"sync", FALSE, NULL);
g_signal_connect( _sink, "new-sample", G_CALLBACK(onNewBuffer), this);

static GstFlowReturn onNewBuffer (GstAppSink *appsink, gpointer userData)
    {
        h265msg::h265 msg;                                  // A rosmsg to
carry h.265 byte-stream frame
        GstMapInfo map;
        GstSample *sample;
        g_signal_emit_by_name(appsink, "pull-sample", &sample);
        if (sample){
            GstBuffer *buffer = gst_sample_get_buffer(sample);
            if (gst_buffer_map (buffer, &map, GST_MAP_READ)) {
                msg.data.resize( map.size );
                memcpy( &msg.data[0], map.data, map.size );
                gst_buffer_unmap(buffer, &map);
            }
            msg.header.stamp = ros::Time::now();
            msg.presentation_ts = buffer->pts;
            msg.decoding_ts = buffer->dts;
            msg.duration = buffer->duration;
            msg.offset = buffer->offset;
            msg.offset_end = buffer->offset_end;
            _pub.publish(msg);                             // publish the
msg on network for 2nd appsrc application

            gst_sample_unref(sample);
            return GST_FLOW_OK;
        }
        return GST_FLOW_ERROR;
    }


*Appsrc*
_source = gst_element_factory_make ("appsrc", "appsrc");
g_object_set (_source, "caps", gst_caps_new_simple("video/x-h265",
                                                                    
"stream-format", G_TYPE_STRING, "byte-stream",
                                                                    
"alignment", G_TYPE_STRING, "au",
                                                                    
"width", G_TYPE_INT, 1280,
                                                                    
"height", G_TYPE_INT, 720,
                                                                    
"pixel-aspect-ratio", GST_TYPE_FRACTION, 1, 1,
                                                                    
"framerate", GST_TYPE_FRACTION, 25, 1,
                                                                     NULL
                                                                     ),
                                 "stream-type", 0,
                                 "format", GST_FORMAT_TIME,
                                 "min-latency", 0,
                                 "max-latency", 1000000,
                                 "do-timestamp", TRUE,
                                 //"is-live", TRUE,                  // if
is-live is true, it displays only 1 frame per second
                                 NULL);


void getBuffer(const h265msg::h265ConstPtr &msg)
    {
            GstBuffer *buffer = gst_buffer_new_allocate (NULL,
msg->data.size(), NULL);
            gst_buffer_fill(buffer, 0, &msg->data[0], msg->data.size());
            
            GST_BUFFER_PTS (buffer) = msg->presentation_ts;
            GST_BUFFER_DURATION (buffer) = msg->duration;
            GST_BUFFER_DTS(buffer) = msg->decoding_ts;
            GST_BUFFER_OFFSET(buffer) = msg->offset;
            GST_BUFFER_OFFSET_END(buffer) = msg->offset_end;
             
            GstFlowReturn ret;
            g_signal_emit_by_name(_source, "push-buffer", buffer, &ret);
            gst_buffer_unref (buffer);
    }




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