SURROUND is more to spec according to the FIXME comments, so add this. Also add SIDE for 5 and 5.1 because of ffmpeg compatibility, because the following pipeline downmixes to mono otherwise: gst-launch-1.0 audiotestsrc num-buffers=1 ! audio/x-raw, channels=6 ! avenc_ac3 ! avdec_ac3 ! audioconvert ! fdkaacenc ! fakesink -v Fixes #1327 Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1352>