Support float in dpx

[Carl Eugen Hoyos]

​http://samples.ffmpeg.org/V-codecs/dpx/bunny.dpx
​http://thread.gmane.org/gmane.comp.video.ffmpeg.libav.user/15090/focus=15110
Gonzalo kindly provided a dpx image containing floating point values.
Depends on ticket #3657

$ ffmpeg -i bunny.dpx
ffmpeg version 3.0.git-dev-dev-486-g6f5048f Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  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
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
[dpx @ 0x3677820] Depth 32 is not implemented. Update your FFmpeg version to the newest one from Git. If the problem still occurs, it means that your file has a feature which has not been implemented.
[dpx_pipe @ 0x3676280] Stream #0: not enough frames to estimate rate; consider increasing probesize
[dpx_pipe @ 0x3676280] decoding for stream 0 failed
[dpx_pipe @ 0x3676280] Could not find codec parameters for stream 0 (Video: dpx, none, 1280x720): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
bunny.dpx: could not find codec parameters
Input #0, dpx_pipe, from 'bunny.dpx':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: dpx, none, 1280x720, 25 tbr, 25 tbn, 25 tbc
At least one output file must be specified

[Elon Musk]

Doesnt look like float at all, also it is produced by imagemagick thus it explain why file is invalid.

[Carl Eugen Hoyos]

The sample file has four components, the first one being an alpha channel which contradicts what the dpx specification says. The alpha channel appears to use 32bit integer values.

[Elon Musk]

This have been properly implemented. Use ​https://github.com/thorfdbg/difftest_ng for encoding float in DPX instead.