[Flac] Re: FLAC: ERROR, MD5 signature mismatch

[Josh Coalson]

--- Harry Sack <tranzedude at gmail.com> wrote:
> 2007/7/25, Josh Coalson <xflac at yahoo.com>:
> >
> > --- Harry Sack <tranzedude at gmail.com> wrote:
> > > 2007/7/25, Harry Sack <tranzedude at gmail.com>:
> > > >
> > > > Hi
> > > >
> > > > I have downloaded a FLAC file somewhere and when trying to
> decode
> > > it to
> > > > WAV it gives the error message: ERROR, MD5 signature mismatch
> > > > So my question is now: are FLAC files that give the error
> message
> > > above
> > > > still decodable to WAV (and how can you do this, because
> flac.exe
> > > doesn't
> > > > want to decode the file), even if there is a MD5 signature
> > > mismatch, or is
> > > > this not possible at all?
> >
> > if that is the only error given even when decoded with -F, then
> > it got all the samples back.  they are also highly likely to be
> > the same samples that were encoded.  most likely they were encoded
> > on a machine with bad hardware (bad ram, aggressive overclocking),
> > less likely is that the file was corrupted or tampered with.
> 
> But how is it possible then the FLAC encoder allows files which have
> a bad
> resulting MD5 to be encoded? Is it because of the bad ram, ... this
> incorrect MD5 is not detected during encoding?

it happens like this, x.wav gets encoded with flac.exe on a machine
with bad ram.  flac.exe reads some audio data from x.wav into memory
and encodes it.  samples are buffered to md5 checksummer which writes
intermediate checksum to bad memory.  md5 is corrupted but samples
were encoded ok.  the user will not know unless the --verify option
was used during encoding.

> Can you also give me an example of an error message that would occur
> when the file is corrupted?

you would get errors about lost sync, frame crc mismatch, bad header,
or unparseable stream.

Josh



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