There’s one thing I like in Libav audio design and that’s planar audio. There’s one thing I don’t like about it and that’s handling multichannel audio. As a project with roots intermingled with MPlayer, it has followed M$ definition of multichannel audio and since many multichannel codecs have their own channel order lavc decoders have to define channel reordering tables. And it gets hairier when you have dynamic channel configuration (i.e. not one of the static channels configurations but rather a channel mask defining what channels are present or not). It gets especially fun with codecs that have extensions to the base 5.1 format that redefine existing channels and add new ones (like D*lby and DT$ codecs).
My proposal is that multichannel codecs should not bother with what the library considers The Only True Layout but rather export channel map along with the channel data and let the conversion library figure it out (shuffling pointers is not hard you know).
P.S. It’s hard to blame lu_zero for the current Libav situation but I still shall do it.