[ogg-dev] Fixing ogg vorbis corruption caused by bad metadata

[Adam Rosi-Kessel]

ogg.k.ogg.k at googlemail.com wrote, on 7/14/2009 7:16 AM:
>> easy to replace. The second packet is the metadata, which we can lose.
>> It's just the third packet that needs to be reconstructed. After that,
>> you could start at any packet division in the rest of the file and it
>> would play fine? So this generic restore tool that I'm positing would
>> just need to try every known codebook set until a valid file was
>> produced? How hard would that be?
> You'd need to renumber and regenerate CRCs. rogg might do all that
> (a set of tools somewhere on svn.xiph.org).
>> What I'm puzzled by, based on the information above, is why my attempted
>> fixes haven't worked: pick a valid ogg vorbis file that I believe was
>> ripped with the same tool around the same time, swap in the first three
>> packets from that file, modify the serial number to match the new file.
>> Thus far this technique hasn't actually fixed any files.
> CRCs ? If they're wrong (and they'd become wrong if you fiddle with the
> serial number without regenerating them), libogg will ignore the page.

Thank you! I'd never heard of rogg. That definitely gets me one step 
closer to a solution. Taking a file where I had substituted the header 
from a good ogg into the "bad" ogg, and then using rogg to fix the crc, 
I now have a playable file. What's odd is it starts out, for about a 
second, as audible and normal, and then the audio is scrambled -- 
perhaps a bitrate issue?

Here's a sample of the result of this process:

http://adam.rosi-kessel.org/bugs/liboggz/484/fixed_with_rogg.ogg

So I think this might just need a little more tweaking to be turned into 
an automated fix script. Any ideas based on that file exactly what is 
wrong and how to correct it?

Adam