This is based on a procedure to implement the filterbank on the DCT-IV described in
Hsu, H.W. et al. "A Complex Quadrature Mirror Filterbanks for MPEG-4 HE-AAC"
http://sites.google.com/site/wenchiehlee1020/Papers/ComplexFB_AES_121paper144.pdf

Originally committed as revision 23516 to svn://svn.ffmpeg.org/ffmpeg/trunk