The boilerplate states that the files are under LGPL,
but refer the user to the GPL at one place.
These files were (re)implemented specifically for FFmpeg.
The planar/packed switch and the packing_formats list is no longer
required, since the planar/packed information is now stored in the sample
format enum.
This is technically a major API break, possibly it should be not too
painful as we marked the audio filtering API as unstable.