Adam Rosi-Kessel
2009-Jun-21 13:29 UTC
[ogg-dev] Fixing ogg vorbis corruption caused by bad metadata
Conrad Parker wrote, on 6/20/2009 10:24 PM:>> How about another approach -- is there a tool that will verify the page >> checksums? oggz-validate doesn't seem to do this. If the page checksums >> are okay, then doesn't that suggest the streams are also recoverable? > If the page checksums are bad then the page will get rejected by > libogg, and oggz-validate won't even see it (or its packets). "hogg > dumpraw" will at least show the page CRC and segment table, before > verifying the CRC, which could be useful.Does it actually check the CRC, or is there some way for me to do so? I see the output from hogg dumpraw, but am not sure how to interpret it. In other news, the MediaMonkey developers believe this is a bug in a (possibly) older version of vorbis_comment_add_tag(): http://www.ventismedia.com/mantis/view.php?id=5809 Does this seem right and/or shed any light on how to undo the damage? Adam
Adam Rosi-Kessel
2009-Jun-25 03:24 UTC
[ogg-dev] Fixing ogg vorbis corruption caused by bad metadata
Adam Rosi-Kessel wrote, on 6/21/2009 9:29 AM:> Conrad Parker wrote, on 6/20/2009 10:24 PM: >>> How about another approach -- is there a tool that will verify the page >>> checksums? oggz-validate doesn't seem to do this. If the page checksums >>> are okay, then doesn't that suggest the streams are also recoverable? >> If the page checksums are bad then the page will get rejected by >> libogg, and oggz-validate won't even see it (or its packets). "hogg >> dumpraw" will at least show the page CRC and segment table, before >> verifying the CRC, which could be useful. > > Does it actually check the CRC, or is there some way for me to do so? I > see the output from hogg dumpraw, but am not sure how to interpret it. > > In other news, the MediaMonkey developers believe this is a bug in a > (possibly) older version of vorbis_comment_add_tag(): > > http://www.ventismedia.com/mantis/view.php?id=5809 > > Does this seem right and/or shed any light on how to undo the damage?One other potentially interesting observation -- Ogg::Vorbis::Header::PurePerl has no trouble reading the headers on these corrupted files (and outputting the contents correctly), while Ogg::Vorbis::Header dies. Unfortunately, the PurePerl module doesn't have any functions implemented to delete metadata -- if it did, I would try using that to clear out the tags. But I wonder if the difference between the two implementations provides a clue for how to fix this. I also took a stab at hacking on hogg, but I couldn't figure out what was different about what you were recommending than the existing sort function there. Adam
Monty Montgomery
2009-Jun-25 17:10 UTC
[ogg-dev] Fixing ogg vorbis corruption caused by bad metadata
Vorbose -v reports the following for the beginning of the file: INFO page: Capture pattern OggS, format version 0 Flags: first page of logical stream Granule position: 0x0000000000000000 Stream serialno : 0x490f5cff Sequence number : 0 Checksum : 0xee9c02b9 Total segments : 1 Total packets : 1 completed ( 30) info header: Vorbis identification header parsed: Stream version : 0 Output channels : 2 Output sample rate : 44100 Hz Bitrate targets : unset/224000/unset Block sizes : 256/2048 samples WARN stream: 53638 bytes of garbage before page 1 info stream: All identification header pages parsed. 1 logical stream muxed in this link. INFO page: Capture pattern OggS, format version 0 Flags: packet continued from previous page Granule position: 0x0000000000000000 Stream serialno : 0x490f5cff Sequence number : 13 Checksum : 0xab096acc Total segments : 6 Total packets : 1 completed (1 cont) (255, 255, 255, 255, 255, 113) In short, this file's Ogg encapsulation is corrupt. There's no chance of this being a vorbis_comment_add_tag() bug as that would be corrupt data inside valid Ogg. The Ogg structure itself is invalid here. Monty
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