support PixelCrop* and DisplayWidth Display Height elements of Matroska

[dave rice]

Summary of the bug:

The Matroska spec defines PixelCrop[Bottom|Top|Left|Right] elements as the value of "The number of video pixels to remove at the [top|bottom|left|right] of the image." Presently the values don't appear to be used in the display.

For instance, the attached sample matroska_pixel_crop_test.mkv uses these pixel/crop/display values:
PixelWidth 320
PixelHeight 240
PixelCropBottom 40
PixelCropTop 0
PixelCropLeft 240
PixelCropRight 40
DisplayWidth 320
DisplayHeight 240

Since the image is a 320x240 testsrc image, the display should be cropped so that only one color bar is shown, but instead the whole frame is shown/used. I suggest have a demuxer option to enable/disable the use of PixelCrop* elements when matroska is used.

How to reproduce:

ffmpeg -i matroska_pixel_crop_test.mkv 
ffmpeg version N-44055-g6f5048f Copyright (c) 2000-2016 the FFmpeg developers
  built with Apple LLVM version 7.0.2 (clang-700.1.81)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-opencl --enable-libx264 --enable-libmp3lame --enable-libxvid --enable-libfreetype --enable-libfaac --enable-libass --enable-ffplay --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags=-I/usr/local/Cellar/openjpeg/1.5.2_1/include/openjpeg-1.5 --enable-nonfree --enable-vda
  libavutil      55. 19.100 / 55. 19.100
  libavcodec     57. 27.101 / 57. 27.101
  libavformat    57. 28.100 / 57. 28.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 39.100 /  6. 39.100
  libavresample   3.  0.  0 /  3.  0.  0
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, matroska,webm, from 'matroska_pixel_crop_test.mkv':
  Metadata:
    ENCODER         : Lavf57.28.100
  Duration: 00:00:01.00, start: 0.000000, bitrate: 869 kb/s
    Stream #0:0: Video: ffv1 (FFV1 / 0x31564646), yuv420p, 320x240, SAR 1:1 DAR 4:3, 25 fps, 25 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      ENCODER         : Lavc57.27.101 ffv1
      DURATION        : 00:00:01.000000000
At least one output file must be specified

Another real-world sample with these values is available here: ​http://archive.org/download/dl.icemusic.com/ArashFt.Aysel-AlwaysliveEurovisionSemiFinal2009.-WwW.Myicemusic-IR.mkv. It uses:
PixelWidth: 720
PixelHeight: 576
PixelCropBottom: 4
PixelCropTop = 0
PixelCropLeft = 2
PixelCropRight = 4
DisplayWidth = 1024
DisplayHeight = 576

Thanks

[dave rice]

Matroska file with PixelCrop values set

[Carl Eugen Hoyos]

Should be tested again once ticket #4489 is fixed.