Wav muxer for libffmpeg-custom

Trying to build a firmware including libx264 I enable CONFIG_BUILD_PATENTED=y in global build options. Unfortunately this makes libffmpeg-full lose the libfdk_aac codec.

In an attempt to get it back I switch to libffmpeg-custom. But now wave output seems to get lost. There is not even an entry to select the wav muxer for libffmpeg-custom in menuconfig.

What am I doing wrong?