To be shared with the AGGREGATE handling. Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1384>
Similar to gst_rtmp_output_stream_write_all_bytes_async, but takes a GstBuffer instead of a GBytes. It can also return the number of bytes written, which might be lower in case of an error.
For master, without autotools.