ogg dev - Jul 2009 - Fixing ogg vorbis corruption caused by bad metadata

Conrad Parker wrote, on 7/8/2009 8:20 PM:
>> Anything I can do to keep this on radar? I'm not sure if it is
really a bug
>> -- perhaps at least a wishlist request. Will putting it in a tracker
>> somewhere help?
> yes, a tracker would help.
I'm somewhat confused about the right place to file this--can you 
suggest? There seem to be few separate projects it might belong to.
> At this point it really looks like some pretty bizarre and
> inconsistent corruption, which would probably need some custom tools
> to fix.
Is it impractical to suggest a generic tool that simply starts reading 
an ogg file from the beginning, and once it gets past any corruption it 
outputs the rest as a valid file? For example, if you just split an ogg 
vorbis file in half, and only had the second half, is there no currently 
existing tool, or one that could be easily developed from the existing 
libraries, that would take that second half and make it playable?

I do think these problems are actually not that unusual based on the 
number of unanswered threads from other people I've found around other 
discussion lists on trying to repair broken files. And the corruption is 
completely reproducible with MediaMonkey, a very common metadata tagging 
tool. I understand this is probably MediaMonkey's problem/fault 
(although they seem to use the generic ogg/vorbis libraries for 
metadata), but it does leave the fact that there may be many people with 
this problem or a variant thereof out there.

Adam

>
> Is it impractical to suggest a generic tool that simply starts reading
> an ogg file from the beginning, and once it gets past any corruption it
> outputs the rest as a valid file?
Yes.  Without the first three packets (which hold all the codec
settings and all the instruction how to handle the subsequent packets)
the rest of the stream is gibberish.  Vorbis can't even unpack the
bits without the codebooks packed into the third header.
> For example, if you just split an ogg
> vorbis file in half, and only had the second half, is there no currently
> existing tool, or one that could be easily developed from the existing
> libraries, that would take that second half and make it playable?
...only if it was able to read (and tack on) the first three packets
from the first half.

Monty

Monty Montgomery wrote:
> Yes.  Without the first three packets (which hold all the codec
> settings and all the instruction how to handle the subsequent packets)
> the rest of the stream is gibberish.  Vorbis can't even unpack the
> bits without the codebooks packed into the third header.
Curiosity man here.

Is there a finite set of predetermined codebooks or is the codebook
source dependent?

Erik
-- 
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Erik de Castro Lopo
http://www.mega-nerd.com/