When using nvmultistreamtiler plugin in your pipeline, the multiple streams are merged to one stream. “process_meta” is probed after nvmultistreamtiler plugin, so it can only detect one stream.
Either disable nvmultistreamtiler or move “process_meta” before nvmultistreamtiler and after “nvstreammux”, you can get the separated stream id with “frame_meta->source_id”.