[FFmpeg-trac] #11128(avcodec:new): FFV1 encodes files that fail strict 3rd-party MediaConch validation when using 2-pass encoding

[FFmpeg]

#11128: FFV1 encodes files that fail strict 3rd-party MediaConch validation when
using 2-pass encoding
-------------------------------------+-------------------------------------
             Reporter:  James        |                     Type:  defect
  Johnston                           |
               Status:  new          |                 Priority:  normal
            Component:  avcodec      |                  Version:
                                     |  unspecified
             Keywords:  FFV1 ffv1    |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 **Summary of the bug:**

 FFmpeg / FFV1 encodes FFV1 slices that fail multiple !MediaConch
 validation rules when using 2-pass encoding.

 How to reproduce:

 This is on Windows 10 64-bit with nightly build "ffmpeg-2024-08-04-git-
 eb3cc508d8-full_build" downloaded from https://www.gyan.dev/ffmpeg/builds/

 1.  Download the attached !TestVideo.avi file (it has HuffYUV encoding and
 PCM audio).

 2.  Run this FFmpeg command:

 {{{
 # Input file is AVI container with HuffYUV video and PCM audio; probably
 many other inputs will work
 ffmpeg -i TestVideo.avi -map 0 -vf setfield=tff -c:a flac -c:v ffv1 -level
 3 -g 1 -context 1 -coder 2 -slicecrc 1 -passlogfile TestVideo.log -pass 1
 -aspect 4:3 -pix_fmt yuv422p TestVideo.mkv

 # Second pass
 ffmpeg -i TestVideo.avi -map 0 -vf setfield=tff -c:a flac -c:v ffv1 -level
 3 -g 1 -context 1 -coder 2 -slicecrc 1 -passlogfile TestVideo.log -pass 2
 -aspect 4:3 -pix_fmt yuv422p TestVideo.mkv
 }}}

 3.  Validate the file using !MediaConch (available online/live at
 https://mediaarea.net/MediaConchOnline/checker, download from
 https://mediaarea.net/MediaConch, or your favorite package manager).

 **Expected behavior**

 FFV1 files should pass validation tests with flying colors.

 Note that 1-pass FFV1 files do, in fact, pass.  It is the 2-pass encoding
 that fails.

 **Actual behavior**

 !MediaConch reports these validation failures (also see screenshot):

 {{{
 FFV1-SLICE-SliceContent Tests run: 24 | Results: ❌ | Fail count: 24
 Results: fail ❌
 Name: SliceContent
 Offset: 30925
 Value context:
 /Segment[1]/Cluster[1]/SimpleBlock[1]/Data[1]/Frame[1]/Slice[1]/SliceContent[1]
 Value: (57497 bytes)
 Results: fail ❌
 Name: SliceContent
 Offset: 88430
 Value context:
 /Segment[1]/Cluster[1]/SimpleBlock[1]/Data[1]/Frame[1]/Slice[2]/SliceContent[1]
 Value: (54834 bytes)
 Results: fail ❌
 Name: SliceContent
 Offset: 143272
 Value context:
 /Segment[1]/Cluster[1]/SimpleBlock[1]/Data[1]/Frame[1]/Slice[3]/SliceContent[1]
 Value: (53000 bytes)

 <snip many more>
 }}}

 The validation code for this is located at
 https://github.com/MediaArea/MediaInfoLib/blob/abdbb218b07f6cc0d4504c863ac5b42ecfab6fc6/Source/MediaInfo/Video/File_Ffv1.cpp#L1335-L1336

 {{{
 void File_Ffv1::SliceContent(states &States)
 {
     if (BS->BufferUnderRun || RC->Underrun())
         Element_Error("FFV1-SLICE-SliceContent:1");
 }}}

 It appears there is some kind of underrun condition / incoherency in the
 file.  My guess is this used to be called / was intended to be called the
 otherwise-non-implemented rule "FFV1-SLICE-END", documented at
 https://github.com/MediaArea/MediaConch/blob/d2a4b62ffbaf5475c5c3e82b3e6fc9883a6be592/MetadataDevelopment/ImplementationChecks/FFV1Registry.xml#L203,
 as "Real slice end is met before or after expected slice end" as a
 coherency violation.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11128>
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