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List:       flac
Subject:    Re: [flac] md5 checksum
From:       Josh Coalson <xflac () yahoo ! com>
Date:       2007-10-19 18:57:21
Message-ID: 675694.98993.qm () web60412 ! mail ! yahoo ! com
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--- Harry Sack <tranzedude@gmail.com> wrote:
> 2007/10/19, Josh Coalson <xflac@yahoo.com>:
> >
> > --- Harry Sack <tranzedude@gmail.com> wrote:
> > > hi
> > >
> > > here some questions about the md5 checksum:
> > >
> > > - what happens when the md5 checksum of the decoded audio is
> > > different
> > > of the internally stored checksum due to file corruption ? Will
> > > playing/decoding still be possible (with some error frames) or
> will
> > > playing /decoding be not possible at all (so all audio data is
> lost)?
> >
> > md5 does not affect decoding at all, it is a just a checksum to
> > tell you at the end if it matches the whole audio or not.
> 
> 
> 
> thanks for the answer, but then there is wrong information on some
> sites
> that tell about flac :s.
> There is written the flac decoder doesn't decode the audio at all
> when the
> md5 checksum doesn't match.

that's a feature of flac(.exe) not the decoder.

> > - what happens when the metadata blocks get corrupt? will the audio
> > > part still be decodable even when non-audio blocks are corrupt?
> >
> > yes
> >
> > > - since there is only a md5 checksum on the audio blocks itself,
> what
> > > happens when some wav metadata gets corrupt and you want to
> decode
> > > that data? How can the decoder detect it's corrupt or not because
> > > there is no md5 checksum for this data?
> >
> > depends on the corruption, some kinds are recoverable, some are
> not.
> > read the format spec first and it should become clear.
> 
> 
> 
> Why is there no md5 checksum on the WAV metadata? Because how can
> flac
> otherwise be called a 'lossless' codec when the metadata of the WAV
> file
> can't be guaranteed 100% identical to the original, when there is
> file
> corruption, because there is no md5 checksum on it?

because it's a lossless *audio* codec.  BTW a file cannot checksum
itself, there has to be some part of it immune from the checksum.
if you really need this feature, you can always checksum the whole
file yourself.

Josh


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