Fail init for unknown fft order, to prevent an array overflow
Output sound high-pitched compared to binary. Sample here
http://a1862.g.akamai.net/7/1862/14448/v1/esa.download.akamai.com/13452/qt/ESA_VenusExpress_110K_Stream.mov

Originally committed as revision 4724 to svn://svn.ffmpeg.org/ffmpeg/trunk