[FFmpeg-trac] #7777(undetermined:new): cropdetect values cut too much

[FFmpeg]

#7777: cropdetect values cut too much
-------------------------------------+-------------------------------------
             Reporter:  JouMxyzptlk  |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:

 cropdetect uses modulo for its second parameter, possibly cutting of parts
 of a video instead of  preserving the video with less black bars.

 How to reproduce:

 Testvideo: http://joumxyzptlk.de/tmp/ffplay-autoexit-not-working.mkv
 Actual crop values would be w=1479:h=1079:x=220:y=0 (or codec freindly
 w=1480:h=1080:x=220:y=0)

 {{{
 C:\tmp>c:\prog\ffmpeg\bin\ffmpeg -i ffplay-autoexit-not-working.mkv
 -frames:v 2 -vf cropdetect -f null NUL
 ffmpeg version N-93139-ga9452fe6dc Copyright (c) 2000-2019 the FFmpeg
 developers
   built with gcc 8.2.1 (GCC) 20190212
   configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-
 fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-
 libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame
 --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
 --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr
 --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack
 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2
 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-
 libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa
 --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx
 --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-
 nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt
   libavutil      56. 26.100 / 56. 26.100
   libavcodec     58. 47.102 / 58. 47.102
   libavformat    58. 26.101 / 58. 26.101
   libavdevice    58.  6.101 / 58.  6.101
   libavfilter     7. 48.100 /  7. 48.100
   libswscale      5.  4.100 /  5.  4.100
   libswresample   3.  4.100 /  3.  4.100
   libpostproc    55.  4.100 / 55.  4.100
 Input #0, matroska,webm, from 'ffplay-autoexit-not-working.mkv':
   Metadata:
     ENCODER         : Lavf57.71.100
   Duration: 00:00:24.97, start: 0.020000, bitrate: 3079 kb/s
     Stream #0:0: Video: h264 (High), yuv420p(progressive), 1920x1080 [SAR
 1:1 DAR 16:9], 24.39 fps, 24.39 tbr, 1k tbn, 47.95 tbc (default)
     Metadata:
       DURATION        : 00:00:24.966000000
     Stream #0:1(jpn): Audio: aac (LC), 48000 Hz, stereo, fltp (default)
     Metadata:
       DURATION        : 00:00:24.681000000
 Stream mapping:
   Stream #0:0 -> #0:0 (h264 (native) -> wrapped_avframe (native))
   Stream #0:1 -> #0:1 (aac (native) -> pcm_s16le (native))
 Press [q] to stop, [?] for help
 Output #0, null, to 'NUL':
   Metadata:
     encoder         : Lavf58.26.101
     Stream #0:0: Video: wrapped_avframe, yuv420p, 1920x1080 [SAR 1:1 DAR
 16:9], q=2-31, 200 kb/s, 24.39 fps, 24.39 tbn, 24.39 tbc (default)
     Metadata:
       DURATION        : 00:00:24.966000000
       encoder         : Lavc58.47.102 wrapped_avframe
     Stream #0:1(jpn): Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
 (default)
     Metadata:
       DURATION        : 00:00:24.681000000
       encoder         : Lavc58.47.102 pcm_s16le
 [Parsed_cropdetect_0 @ 000001dd37f3a900] x1:220 x2:1698 y1:0 y2:1078
 w:1472 h:1072 x:224 y:4 pts:381 t:0.381000 crop=1472:1072:224:4
 frame=    2 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.74 bitrate=N/A
 speed=22.3x
 video:1kB audio:140kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 }}}

 Detected crop values are: w=1472:h=1072:x=224:y=4
 Expected crop values are: w=1480:h=1080:x=220:y=0

 Even when using `-vf "cropdetect=24:2:0"` I get w=1478:h=1078:x=220:y=0 -
 but at least X and Y are sane values when using modulo 2.
 `-vf "cropdetect=24:128:0"` results in w=1408:h=1024:x=256:y=28

 Handbrake suffers from the same issue, so fixing it in ffmpeg might fix it
 in the next Handbrake version automatically...

 We need an option to prefer smaller black borders over killing parts of
 the video.
 The suggested fix to keep compatibility: A fourth parameter in cropdetect,
 set to "1" and it prefers keeping small black bars instead of clipping the
 actual content.
 My current workaround for `cropdetect=24:2:0` is to add 2 to width and
 height of the detected crop values before using them in the subsequent
 ffmpeg encoding command.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/7777>
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