Get a GstBuffer/GstMemory/GstSample from an element in running pipeline

Question

I need to randomly access image data in a running pipeline. Something like gst_base_sink_get_last_sample() but not for a sink element placed at the end of the pipeline. I need to inspect passing data in the middle of the pipeline while running, for example inspect the input buffer to the glupload. I also can not add tee to the pipeline to make a fork and send that to fakesink as tee has overheads of data copy for each frame. Is there any method I can use to extract current buffer/memory/sample of data in a PLAYING element in gstreamer pipeline?

Pipeline:

Answer 1

Thanks to @FlorianZwoch, I made it using pad probe. Every time I need to get access to data to probe it, I add a probe to any pad I want like this:

GstPad* pad = gst_element_get_static_pad(v4l2convert, "src");
gst_pad_add_probe(pad, GST_PAD_PROBE_TYPE_BUFFER, probe_callback, NULL, NULL);
gst_object_unref(pad);

and then in the callback function I can access data using these lines of code:

GstPadProbeReturn Gstreamer::probe_callback(
    GstPad* pad, GstPadProbeInfo* info, gpointer user_data)
{
    Q_UNUSED(user_data);
    gst_println("callback called");

    GstBuffer* buffer = gst_pad_probe_info_get_buffer(info);  // No need to unref later [see docs]
    GstCaps*   caps   = gst_pad_get_current_caps(pad);

    if (!buffer || !caps)
    {
        g_printerr("Probe callback failed to fetch valid data.");
        goto label_return;
    }

    // Consume data here

    return GST_PAD_PROBE_REMOVE;
}