Then it might be reasonable to make this note in the openmax docs at the https://github.com/raspberrypi/firmware
that audio decoding and encoding is not implemented as described in the respective components, or is it? I lost some great deal of time fiddling with these components, looking around and searching for information and finally came to the indefinite (not clearly confirmed) conclusion that current audio components do not support any codecs at all.
However if source code was provided or at least docs and appropriate toolchain for compiling and not the binary blobs for the GPU I think this might have solved licencing issues as is the matter with ffmpeg and the non-free aac codecs for example.
It might have been discussed somewhere but I haven't come across yet any information that drives the reasoning behind hiding the above information on the GPU.