qdm2: 8bps mode decodes with audiable distortions

[ami_stuff]

similar problem can be reproduced with file from ticket #742

C:\>ffmpeg -i 44kHz_8kbps.aif out.wav
ffmpeg version N-45867-g3318d6b Copyright (c) 2000-2012 the FFmpeg developers
  built on Oct 23 2012 02:39:33 with gcc 4.5.0 (GCC) 20100414 (Fedora MinGW 4.5.
0-1.fc14)
  configuration: --prefix=/var/www/users/research/ffmpeg/snapshots/build --arch=
x86 --target-os=mingw32 --cross-prefix=i686-pc-mingw32- --cc='ccache i686-pc-min
gw32-gcc' --enable-w32threads --enable-memalign-hack --enable-runtime-cpudetect
--enable-cross-compile --enable-static --disable-shared --extra-libs='-lws2_32 -
lwinmm -lpthread' --extra-cflags='--static -I/var/www/users/research/ffmpeg/snap
shots/build/include' --extra-ldflags='-static -L/var/www/users/research/ffmpeg/s
napshots/build/lib' --enable-bzlib --enable-zlib --enable-gpl --enable-version3
--enable-nonfree --enable-libx264 --enable-libspeex --enable-libtheora --enable-
libvorbis --enable-libfaac --enable-libxvid --enable-libopencore-amrnb --enable-
libopencore-amrwb --enable-libmp3lame --enable-libvpx --disable-decoder=libvpx
  libavutil      51. 77.100 / 51. 77.100
  libavcodec     54. 68.100 / 54. 68.100
  libavformat    54. 33.100 / 54. 33.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 20.104 /  3. 20.104
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
Guessed Channel Layout for  Input Stream #0.0 : mono
Input #0, aiff, from '44kHz_8kbps.aif':
  Duration: 00:00:00.00, start: 0.000000, bitrate: 33509 kb/s
    Stream #0:0: Audio: qdm2 (QDM2 / 0x324D4451), 44100 Hz, mono, s16, 8 kb/s
Output #0, wav, to 'out.wav':
  Metadata:
    ISFT            : Lavf54.33.100
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono, s16,
705 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (qdm2 -> pcm_s16le)
Press [q] to stop, [?] for help
size=     400kB time=00:00:00.09 bitrate=34869.7kbits/s
video:0kB audio:400kB subtitle:0 global headers:0kB muxing overhead 0.019531%

[ami_stuff]

more samples:

​http://www.datafilehost.com/download-61de3d62.html

[Carl Eugen Hoyos]

Fixed by Roberto Togni, thank you for the samples!