ALLOCATION_QUERY via tee

Plugin and library development
1

Hi there,

I’m looking some example how to handle allocation query in the pipelines with tee.
My pipeline looks like this:

fakesrc ! elem_a ! tee name=tee_1 ! elem_b ! fakesink tee_1. ! elem_c ! fakesink

I want to send allocation query from elem_a to elem_b and elem_c respectively, then handle them in _b and _c (add some metadata to them) and
then obtain metadata in _a. My current implementation (took an example from here: Memory allocation ) works perfectly fine with 1-1 connection but failing once I’m adding the second branch.

In short, the current implementation looks like:

elem_a:

[gst_elem_a_state_change]
query = gst_query_new_allocation (caps, TRUE);
if (gst_pad_peer_query (elem_a->srcpad, query) {
  if (gst_query_find_allocation_meta (query, GST_VIDEO_META_API_TYPE, &video_idx)) {
    gst_query_parse_nth_allocation_meta (query, video_idx, &params);
    ...
  }
}


elem_b/elem_c:
if (GST_QUERY_TYPE(query) == GST_QUERY_ALLOCATION) {
    GstStructure * params = gst_structure_new ("allocation-meta", "myparam", G_TYPE_STRING, "my_value", NULL);
    gst_query_add_allocation_meta (query, GST_VIDEO_META_API_TYPE, params);
} else {
    gst_pad_query_default (pad, parent, query);
 }
  return TRUE;

I’m able to receive GST_QUERY_ALLOCATION in elem_b and elem_c, but I’m getting an error while parsing allocation meta in elem_a.

3

Allocation meta parameters had been unsupported for many years due to the lack of code to aggredate multiple paramters together (you can only add API once in the allocation query, which imply only one parameter). Since 1.26 we have introduced gst_meta_api_type_set_params_aggregator() that let metadta data implementor the ability to aggregate the parameters, and tee is now using it.