[FFmpeg-trac] #2452(undetermined:new): decoding yuv420p to rgb shifts luminance down

[FFmpeg]

#2452: decoding yuv420p to rgb shifts luminance down
-------------------------------------+-------------------------------------
             Reporter:  burek        |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------

Comment (by glopes):

 Thanks for asking, actually! I just tried with the latest build (ffmpeg
 version N-55159-gf118b41) and it turns out now it's not even possible to
 get the correct luminance values by using the first command line!!

 I don't know what changed about pix_fmt gray decoding from yuv420p, but
 now things are even worse as I have currently no way of recovering the
 correct luminance from my recorded videos... data loss is now a serious
 possibility...

 Last known working version is ffmpeg version N-51639-g7775992.

 Here's the output from the two commands now:

 gray pix_fmt:
 {{{
 ffmpeg -ss 0.5 -i video.avi -vframes 1 -t 1 -s 1280x680 -pix_fmt gray
 gray.bmp
 }}}

 {{{
 ffmpeg version N-55159-gf118b41 Copyright (c) 2000-2013 the FFmpeg
 developers
   built on Aug  1 2013 18:08:30 with gcc 4.7.3 (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-libcaca --enable-
 libfreetyp
 e --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame
 --ena
 ble-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
 --enable-l
 ibopus --enable-librtmp --enable-libschroedinger --enable-libsoxr
 --enable-libsp
 eex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-
 libvo-
 amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-
 libxavs --
 enable-libxvid --enable-zlib
   libavutil      52. 40.100 / 52. 40.100
   libavcodec     55. 19.100 / 55. 19.100
   libavformat    55. 12.102 / 55. 12.102
   libavdevice    55.  3.100 / 55.  3.100
   libavfilter     3. 82.100 /  3. 82.100
   libswscale      2.  4.100 /  2.  4.100
   libswresample   0. 17.103 /  0. 17.103
   libpostproc    52.  3.100 / 52.  3.100
 Input #0, avi, from 'video.avi':
   Metadata:
     encoder         : Lavf53.22.0
   Duration: 00:00:13.59, start: 0.000000, bitrate: 5596 kb/s
     Stream #0:0: Video: mpeg4 (Simple Profile) (FMP4 / 0x34504D46),
 yuv420p, 128
 0x680 [SAR 1:1 DAR 32:17], 120 fps, 120 tbr, 120 tbn, 120 tbc
 File 'gray.bmp' already exists. Overwrite ? [y/N] y
 Output #0, image2, to 'gray.bmp':
   Metadata:
     encoder         : Lavf55.12.102
     Stream #0:0: Video: bmp, gray, 1280x680 [SAR 1:1 DAR 32:17], q=2-31,
 200 kb/
 s, 90k tbn, 120 tbc
 Stream mapping:
   Stream #0:0 -> #0:0 (mpeg4 -> bmp)
 Press [q] to stop, [?] for help
 frame=    1 fps=0.0 q=-1.0 Lsize=N/A time=00:00:00.00 bitrate=N/A
 video:851kB audio:0kB subtitle:0 global headers:0kB muxing overhead
 -100.002524%
 }}}

 bgr24 pix_fmt:
 {{{
 ffmpeg -ss 0.5 -i video.avi -vframes 1 -t 1 -s 1280x680 -pix_fmt bgr24
 rgb.bmp
 }}}

 {{{
 ffmpeg version N-55159-gf118b41 Copyright (c) 2000-2013 the FFmpeg
 developers
   built on Aug  1 2013 18:08:30 with gcc 4.7.3 (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-libcaca --enable-
 libfreetyp
 e --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame
 --ena
 ble-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
 --enable-l
 ibopus --enable-librtmp --enable-libschroedinger --enable-libsoxr
 --enable-libsp
 eex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-
 libvo-
 amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-
 libxavs --
 enable-libxvid --enable-zlib
   libavutil      52. 40.100 / 52. 40.100
   libavcodec     55. 19.100 / 55. 19.100
   libavformat    55. 12.102 / 55. 12.102
   libavdevice    55.  3.100 / 55.  3.100
   libavfilter     3. 82.100 /  3. 82.100
   libswscale      2.  4.100 /  2.  4.100
   libswresample   0. 17.103 /  0. 17.103
   libpostproc    52.  3.100 / 52.  3.100
 Input #0, avi, from 'video.avi':
   Metadata:
     encoder         : Lavf53.22.0
   Duration: 00:00:13.59, start: 0.000000, bitrate: 5596 kb/s
     Stream #0:0: Video: mpeg4 (Simple Profile) (FMP4 / 0x34504D46),
 yuv420p, 128
 0x680 [SAR 1:1 DAR 32:17], 120 fps, 120 tbr, 120 tbn, 120 tbc
 File 'rgb.bmp' already exists. Overwrite ? [y/N] y
 Output #0, image2, to 'rgb.bmp':
   Metadata:
     encoder         : Lavf55.12.102
     Stream #0:0: Video: bmp, bgr24, 1280x680 [SAR 1:1 DAR 32:17], q=2-31,
 200 kb
 /s, 90k tbn, 120 tbc
 Stream mapping:
   Stream #0:0 -> #0:0 (mpeg4 -> bmp)
 Press [q] to stop, [?] for help
 frame=    1 fps=0.0 q=-1.0 Lsize=N/A time=00:00:00.00 bitrate=N/A
 video:2550kB audio:0kB subtitle:0 global headers:0kB muxing overhead
 -100.000843
 %
 }}}

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2452#comment:5>
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