Cineform decoder alpha channel regression

[mkver]

Commit c64c97b972c7325a71440a352a7d541a8c92b2da has added support for alpha channel decoding in Cineform HD (thereby fixing #6265), but commit 9cefb9e7ec508900ba147e6977590f03456aa15c broke it again (the function process_alpha introduced in the first commit is now not even used any more -- thanks to Clang for reporting this). The sample cineform_rgba_12b.mov from #6265 now decodes as before c64c97b972c7325a71440a352a7d541a8c92b2da.

% ffmpeg -i cineform_rgba_12b.mov cin.git.master.png
ffmpeg version N-93777-g0b5c93b276 Copyright (c) 2000-2019 the FFmpeg developers
  built with clang version 9.0.0 (trunk 359932) (llvm/trunk 359941)
  configuration: --disable-debug
  libavutil      56. 26.101 / 56. 26.101
  libavcodec     58. 52.101 / 58. 52.101
  libavformat    58. 27.103 / 58. 27.103
  libavdevice    58.  7.100 / 58.  7.100
  libavfilter     7. 50.100 /  7. 50.100
  libswscale      5.  4.100 /  5.  4.100
  libswresample   3.  4.100 /  3.  4.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'cineform_rgba_12b.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    creation_time   : 2017-03-25T12:27:41.000000Z
  Duration: 00:00:00.04, start: 0.000000, bitrate: 278876 kb/s
    Stream #0:0(eng): Video: cfhd (CFHD / 0x44484643), gbrap12le(10 bpc, bt709, progressive), 1920x1080, 76015 kb/s, SAR 1:1 DAR 16:9, 24 fps, 24 tbr, 24 tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2017-03-25T12:27:41.000000Z
      handler_name    : Apple Video Media Handler
      encoder         : GoPro CineForm
      timecode        : 00:00:00:00
    Stream #0:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, stereo, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2017-03-25T12:27:41.000000Z
      handler_name    : Apple Sound Media Handler
      timecode        : 00:00:00:00
    Stream #0:2(eng): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
    Metadata:
      creation_time   : 2017-03-25T12:27:41.000000Z
      handler_name    : Time Code Media Handler
      timecode        : 00:00:00:00
Stream mapping:
  Stream #0:0 -> #0:0 (cfhd (native) -> png (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'cin.git.master.png':
  Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    encoder         : Lavf58.27.103
    Stream #0:0(eng): Video: png, rgba64be, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 24 fps, 24 tbn, 24 tbc (default)
    Metadata:
      creation_time   : 2017-03-25T12:27:41.000000Z
      handler_name    : Apple Video Media Handler
      timecode        : 00:00:00:00
      encoder         : Lavc58.52.101 png
frame=    1 fps=0.5 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A speed=0.0224x    
video:8221kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

[Carl Eugen Hoyos]

Fixed by Paul in 2edb2627597d99fcad7f6932e7c45f6169250db5