Support colourspace conversion into gbrp16

[LordHDL]

Summary of the bug: Cannot use gbrp16le to produce a video with 16-bit depth. gbrp14le and lower all work fine.
How to reproduce: Record a rawvideo file and attempt to encode it with ffv1 using -pix_fmt gbrp16le.

Last login: Thu Oct 13 09:56:18 on ttys000
HDLs-MacBook-Pro:~ HDL$ ffmpeg -i /Users/HDL/Desktop/Fusion.mov -c:v ffv1 -level 3 -pix_fmt gbrp16le -c:a copy ~/Desktop/gbrp16.nut
ffmpeg version N-81960-g1bda0ee-tessus Copyright (c) 2000-2016 the FFmpeg developers
  built with Apple LLVM version 8.0.0 (clang-800.0.38)
  configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --as=yasm --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-libschroedinger --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzmq --enable-version3 --disable-ffplay --disable-indev=qtkit --disable-indev=x11grab_xcb
  libavutil      55. 32.100 / 55. 32.100
  libavcodec     57. 61.100 / 57. 61.100
  libavformat    57. 51.103 / 57. 51.103
  libavdevice    57.  0.102 / 57.  0.102
  libavfilter     6. 63.100 /  6. 63.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  2.100 /  2.  2.100
  libpostproc    54.  0.100 / 54.  0.100
Guessed Channel Layout for Input Stream #0.1 : stereo
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/HDL/Desktop/Fusion.mov':
  Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    creation_time   : 2016-10-13T11:06:59.000000Z
  Duration: 00:00:43.68, start: 0.000000, bitrate: 148727 kb/s
    Stream #0:0(eng): Video: rawvideo (raw  / 0x20776172), argb, 320x240, 147132 kb/s, 59.87 fps, 60 tbr, 6k tbn, 6k tbc (default)
    Metadata:
      creation_time   : 2016-10-13T11:06:59.000000Z
      handler_name    : Apple Alias Data Handler
      encoder         : None
    Stream #0:1(eng): Audio: pcm_s16be (lpcm / 0x6D63706C), 48000 Hz, stereo, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2016-10-13T11:06:59.000000Z
      handler_name    : Apple Alias Data Handler
Impossible to convert between the formats supported by the filter 'Parsed_null_0' and the filter 'auto-inserted scaler 0'
Error opening filters!
HDLs-MacBook-Pro:~ HDL$ 

[Carl Eugen Hoyos]

Fixed by Paul B Mahol in 6427c9ffee347306d0b00ef94d8cac70babc530c