Encoding RGB huffyuv looses the alpha channel

[Carl Eugen Hoyos]

​http://samples.mplayerhq.hu/V-codecs/HuffYUV/camera2_hfyu32.avi contains a (useful) alpha channel that is decoded correctly by FFmpeg.
Re-encoding the file to huffyuv (or ffvhuff) looses the alpha channel.

$ ffmpeg -i camera2_hfyu32.avi -vcodec huffyuv out.avi
ffmpeg version N-34971-gfca85ce, Copyright (c) 2000-2011 the FFmpeg developers
  built on Nov 19 2011 00:44:40 with gcc 4.3.2 [gcc-4_3-branch revision 141291]
  configuration:
  libavutil    51. 26. 0 / 51. 26. 0
  libavcodec   53. 35. 0 / 53. 35. 0
  libavformat  53. 20. 0 / 53. 20. 0
  libavdevice  53.  4. 0 / 53.  4. 0
  libavfilter   2. 49. 0 /  2. 49. 0
  libswscale    2.  1. 0 /  2.  1. 0
[avi @ 0x8e16a80] parser not found for codec huffyuv, packets or times may be invalid.
Input #0, avi, from 'camera2_hfyu32.avi':
  Duration: 00:00:01.20, start: 0.000000, bitrate: 73500 kb/s
    Stream #0:0: Video: huffyuv (HFYU / 0x55594648), bgra, 512x512, 25 tbr, 25 tbn, 25 tbc
[buffer @ 0x8e1e960] w:512 h:512 pixfmt:bgra tb:1/1000000 sar:0/1 sws_param:
[huffyuv @ 0x8e1e2e0] using huffyuv 2.2.0 or newer interlacing flag
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf53.20.0
    Stream #0:0: Video: huffyuv (HFYU / 0x55594648), bgra, 512x512, q=2-31, 200 kb/s, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (huffyuv -> huffyuv)
Press [q] to stop, [?] for help
frame=   30 fps=  0 q=0.0 Lsize=   10155kB time=00:00:01.20 bitrate=69327.1kbits/s
video:10149kB audio:0kB global headers:0kB muxing overhead 0.061582%

[Carl Eugen Hoyos]

Fixed by Michael.