oggdemux strips any GstCustomMeta you pass in
Currently if you use an appsrc for example and attach some GstCustomMeta to the GstBuffer (using gst_buffer_add_meta) before passing it in to a pipeline containing the oggdemux element, the oggdemux element strips it out even if it contains the right tags like "audio" while it adds some custom metadata itself which it needs to interface properly with opusdec (and maybe some other) element. Other demuxers like qtdemux do the right thing by making sure they preserve any incoming custom metadata in the buffers before adding their own metadata or just passing the metadata as is using: gst_buffer_copy_into (new_buffer, buffer, GST_BUFFER_COPY_METADATA, 0, -1)