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Subject: Re: Corrupt recorded file

Re: Corrupt recorded file

From: Jens Arnold <arnold-j_at_t-online.de>
Date: Wed, 28 Jan 2009 20:00:43 +0100

On 26.01.2009, Michael Hentschel wrote:

> Here is what happened: I have recorded a concert on my Archos
> Jukebox Recorder 20 V1. Rockbox 3.0.1 created a ~192 MB file
> and the total length displays ~2h 33min. After 38 minutes of
> playback Rockbox and most other MP3 players (Winamp,
> Foobar2000, ...) stop playback. Windows Media-player continues
> playing but starts to skip frames and sounds like
> fast-forwarding. When I run MP3-analysing tools on the file
> (eg. mp3val) they say that after 38 minutes there are no mp3
> frames any more, just garbage.
> I searched the file in a hex editor and indeed after 38
> minutes there are no more proper frame headers. Up to this
> point all headers start like "FF FA" (for MPEG I and Layer
> III) and continue with "?0 64" (where ?0 is the bitrate and
> 44.1 kHz, 64 is joint-stereo and other stuff). Only
> occasionally there is an "FF FA" but then the rest of the
> header doesn't make sense.

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.

There's nothing we can do to avoid this bug; care has been taken
to reduce its occurence as much as possible. There's still the
idea to implement a frame monitor for recording, which would
restart the chip if it finds such a defect. This would result in
a short part missing from the final recording. This hasn't been
implemented yet.

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.

Regards, Jens

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Received on 2009-01-28


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