mjpeg: support 2:1:1 YCbCrK

[ami_stuff]

C:\>ffmpeg -i 2_1_1__12_11_11_YCbCrK.jpg
ffmpeg version N-73189-g7728d23 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.9.2 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
ibilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enab
le-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --ena
ble-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc
 --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enabl
e-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --ena
ble-decklink --enable-zlib
  libavutil      54. 27.100 / 54. 27.100
  libavcodec     56. 45.100 / 56. 45.100
  libavformat    56. 38.102 / 56. 38.102
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 18.100 /  5. 18.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.100 /  1.  2.100
  libpostproc    53.  3.100 / 53.  3.100
[mjpeg @ 034ba060] Unhandled pixel format 0x12111112 bits:8
[image2 @ 034a8c40] decoding for stream 0 failed
[image2 @ 034a8c40] Could not find codec parameters for stream 0 (Video: mjpeg,
none(bt470bg/unknown/unknown), 999x749 [SAR 300:300 DAR 999:749]): unspecified p
ixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
2_1_1__12_11_11_YCbCrK.jpg: could not find codec parameters
Input #0, image2, from '2_1_1__12_11_11_YCbCrK.jpg':
  Duration: 00:00:00.04, start: 0.000000, bitrate: 97180 kb/s
    Stream #0:0: Video: mjpeg, none(bt470bg/unknown/unknown), 999x749 [SAR 300:3
00 DAR 999:749], 25 tbr, 25 tbn, 25 tbc
At least one output file must be specified

[ami_stuff]

2_2_2__21_21_21_YCbCrK.jpg has 0x21212121 pix_fmt id, not sure if it decodes "by luck" or is really supported.

[Balling]

Replying to ami_stuff:

2_2_2__21_21_21_YCbCrK.jpg has 0x21212121 pix_fmt id, not sure if it decodes "by luck" or is really supported.

Yeah, I also cannot see this pixel format, but maybe it was added with this commit: d56c373391d334d3dc29c752955fd17f0cef7ff9