[FFmpeg-trac] #3871(avcodec:new): FFmpeg MD5 output different with same data #2

[FFmpeg]

#3871: FFmpeg MD5 output different with same data #2
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             Reporter:  ahthovaikied  |                    Owner:
                 Type:  defect        |                   Status:  new
             Priority:  normal        |                Component:  avcodec
              Version:  2.2.4         |               Resolution:
             Keywords:  md5 aac h264  |               Blocked By:
             Blocking:                |  Reproduced by developer:  0
Analyzed by developer:  0             |
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Comment (by cehoyos):

 Replying to [comment:5 ahthovaikied]:
 > Replying to [comment:2 cehoyos]:
 > > Could you elaborate on what you are trying to show with your tests?
 > I am trying to calculate the MD5 of media data contained in a file.

 My question was: Why do want to calculate the MD5 of the demuxer output?
 What kind of bugs (problems, regressions) are you hoping to find or to
 avoid?

 > For a same input file, I expect the MD5 calculation to be identical
 across different machines unless I alter the file by adding, removing,
 modifying or reordering streams.

 As said, this is missing several conditions like FFmpeg version and
 compilation options.

 > The MD5 calculation should also be reproducible across different FFmpeg
 versions, otherwise I think it's a bug (fixed or introduced).

 Why?
 As said, behaviour changes are possible without a bug being fixed or
 introduced.
 This is of course different for decoder output if a specification exists
 that requests bitexact output as for H.264 or a sample implementation as
 for VP8.

 > Replying to [comment:2 cehoyos]:
 > > I didn't try to reproduce yet, but at least for some input files you
 can certainly get different md5 outputs with your exact command line if
 you are using different configure lines. The md5 values may also change
 depending on the version you test (again without changing the command
 line). All this cannot be surprising so I wonder now what exactly you want
 to test...
 > I am not following you here. Why should the FFmpeg build configuration
 have any influence on the MD5 produced?

 Since libavformat (the demuxer) depends on libavcodec you shouldn't be
 surprised that demuxers produce different output depending on the
 compilation options used.

 > I do not decode the streams, only feed them through the MD5 calculation.
 If I have the MKV demuxer and the ability to calculate the MD5 in an
 FFmpeg build, it should absolutely ALWAYS produce the same MD5.

 No.

 Concerning the bisect: Did you find a version that produces the output you
 want and a version that produces a different output on the same system and
 with the same compilation options?

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Ticket URL: <https://trac.ffmpeg.org/ticket/3871#comment:7>
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