When the subclass attempts to finish without an explicit `out_buffer`, we take a buffer from our adapter. We need to make this buffer writable before copying the metadata. This led to data races such as in the following pipeline, which randomly messed up the buffer PTS: gst-launch-1.0 -e audiotestsrc timestamp-offset=5555 num-buffers=100 \ ! opusenc ! tee name=t ! queue ! opusparse ! fakesink silent=0 \ t. ! queue ! opusparse ! fakesink silent=0 -v | grep '0000, dur' Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5718>
Base classes ------------ GstBaseSink FIXME: not much point making it operate in pull mode as a generic base class I guess...