The latter is going away in libfdk-aac 2.0.0. Instead, MPEG-style output
is always non-interleaved and WAV-style output is always interleaved.
Earlier libfdk-aac also defaults interleaving accordingly.
Since our reordering looks at the associated PCE indices instead of the
actual channel order, we're agnostic to the mapping.
For https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/issues/825
The buffer data is not always copied in _Fill, and will be
read in _DecodeFrame. We unmap at the end of the function,
whether we get there via failure or early out, and keep a
ref to the buffer to ensure we can use it to unmap the
memory even after _finish_frame is called, as it unrefs
the buffer.
Note that there is an access beyond the allocated buffer,
which is only apparent when playing from souphttpsrc (ie,
not from filesrc). This appears to be a bug in the bit
reading code in libfdkaac AFAICT.
https://bugzilla.gnome.org/show_bug.cgi?id=772186
