This is the maximum amount supported by aacenc. 8-channel output fully works. 16-channel also encodes fine, but codec-utils isn't able to parse its channel config, so output level will not be shown in caps. For that to work, GASpecificConfig parsing needs to be implemented. It's not a critical issue and can be worked on at a later date. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6359>