GstBuffer to a PNG Buffer Not using OpenCV

[RK29]

 GstBuffer* buf = gst_sample_get_buffer(sample);
        GstMapInfo info;
        gst_buffer_map(buf, &info, GST_MAP_READ);

        guint8* dataPtr = info.data;
       GstCaps* caps = gst_sample_get_caps(sample);
   
I want to get the PNG Buffer. using Decodebin not playbin. Not using opencv
So far I tried :   
caps = gst_caps_from_string("image/png");
 to_sample =  gst_video_convert_sample(from_sample, caps,
GST_CLOCK_TIME_NONE, &err);///gst_video_convert_sample does not exists.

Can someonegive a proper example?



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