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Subject: Re: Corrupt recorded file

Re: Corrupt recorded file

From: Michael Hentschel <michael.hentschel_at_gmx.at>
Date: Mon, 09 Feb 2009 10:05:32 +0100

> This is a bug in the chip doing all the MP3 encoding and
> decoding in the Archos Recorders and Ondio FM. When recording,
> it may happen that a few bits from the encoded bitstream get
> lost, so that the mp3 frames are no longer byte aligned, and
> most media players become confused.
>
> All that said, there's a chance to salvage your recording. By
> careful checking with a hex editor, you need to find at which
> position(s) the bit alignment is shifted. Using this information
> it is possible to correct the bitshift, with a simple custom
> tool.
>

Hi Jens,

Indeed I figured this out myself by seeking and following the frame
headers. The VBR didn't make this task easy, I had a lot of 160kbps and
occasionally 192kbps frames. But I found the place where the error
occured. I analyzed the next (corrupted) frame header and found out,
that indeed I had to shift it by 2 bits to the left(!). This was before
your reply, so I was really lucky to spot this fact. After I knew what
the problem was, I searched again in the mail archives and found a post
about exactly this bug in the MAS. I wrote a small tool to do the
bit-shifting, and I had to do this correction a few times (about 5 times
in a 2.5 hrs file). The only supprising thing is, that I always had to
remove bits from the stream (or did I miss a padding flag?).

Anyway, finally the file played well on winamp, however not on
Media-Player and neither in my audio editing software (still something
wrong with Xing-header, CRCs or bit-reservoir???). But I did an analog
rerecording and now I can use it. After all I'm glad I could rescue my
recording. Next time I'll go down with recording quality...

Thanx for your help and I hope this discussion might help others in
similar cases.

regards, Mike

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Received on 2009-02-09


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