[Flac-users] Fingerprint Verification Problem

[Josh Coalson]

--- "Paino, Christopher L YN1(AW) (CPF N0084)" <PainoCL at cpf.navy.mil>
wrote:
> If I am understanding FLAC correctly, the internal MD5 sum is (or can
> be
> )different than the fingerprint file sum.

Yes.

> The internal sum can be
> different
> depending on which compression settings are used, while the audio
> remains
> unchanged.

It's the other way around.  Let me sum up my limited knowledge
about how stuff is seeded:

Shorten:
UserA starts with WAV file
UserA compresses with shorten, default arguments
UserA creates fingerprint by running md5sum on the SHN file
(If the user recompresses with different options or a different
version of shorten, the resulting shorten file will be different
causing the md5sum to be different.)
UserA makes a text file with the MD5 sum and SHN filename
UserB downloads text file and SHN file, runs md5sum on it, and
compares it to the text file.

FLAC:
User starts with WAV file
User compresses with FLAC, any arguments, doesn't matter
FLAC encoder stores MD5 of uncompressed audio internally
(If the user decompresses the FLAC to WAV and reencodes,
even with different versions of flac or different options,
the MD5 sum will be the same).
User makes a text file exporting the internal MD5 sum from
the FLAC file, and the FLAC file name.
UserB downloads the text file and FLAC file, and test it
using flac -t, then exports the MD5 sum from the FLAC file,
and compares it to the text file.

Assuming this is all correct, the extra step for FLAC is
exporting the MD5 sum to compare to the text file, because
flac -t doesn't do it.

It's true this is an extra step than with shorten, but the
tradeoff is that with FLAC the fingerprint survives reencoding,
and it verifies that the encoding was done properly in the
first place.

In any case, if you run flac -t and it passes, the only extra
information you get from comparing the MD5 sum to the text
file is to know if the original seeder put the right text file
together with the right FLAC file.  But if you don't need the
contents of the text file to know if the file was d/l'ed OK,
why do you need the text file at all?

Josh


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