Follow-up from "fdkaacenc: Add missing SURROUND mappings"
The following discussion from !1352 (merged) should be addressed:
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
It seems like a bug that this would downmix to mono. Certainly stereo would be a better choice already, so it seems like there's also something to look at here. Maybe a bug in the audioconvert negotiation code, not sure.
Should at least open an issue about that, maybe with a testcase that still works after this MR was merged.