Flac - Apr 2007 - Room for safe opaque blocks in flac streams? Looking to add error correction to flac.

Is there an obvious safe way to add some extra data to a flac file
that spec decoders will happily ignore?

I'd like to explore creating a tool which will add N extra redundancy
frames at the end which will allow perfect decoding with up to ~N
frames lost in the files. This would allow users to sacrifice a tiny
amount of compression for a substantial increase in file robustness.

This would also create a new potential audience for Flac: people who
don't care about file size but care substantially about file
robustness. A typical flac bloated back to the original wav size could
lose roughly half its blocks and still remain perfectly decodable.

http://planete-bcast.inrialpes.fr/article.php3?id_article=7 has a nice
high performance error correcting library which would work well for
this sort of application.

Gregory,

You might want to move your question over to the Flac-dev mailing list.

A FLAC stream allows for additional metadata, including custom data  
which decoders will skip.  However, metadata must come before the  
audio data, and thus you cannot append it to the end.  You also won't  
be able to interleave redundancy data with the main data, and it  
seems to me like interleaving the data somewhat near it's  
counterparts would make more sense.

The ultimate redundancy technique that I follow is to use flac to cut  
the size in half, and then burn two copies of each FLAC file to my CD- 
R or DVD-R backup.  I'm primarily worried about scratches on the  
disc, so saving each file twice seems to reduce the likelihood of  
data loss.  Not to mention the fact that CD/DVD already have data  
redundancy techniques at two different levels of coding.  I don't  
really feel like there is much need for more than that.

Brian Willoughby
Sound Consulting


On Apr 1, 2007, at 20:01, Gregory Maxwell wrote:

Is there an obvious safe way to add some extra data to a flac file
that spec decoders will happily ignore?

I'd like to explore creating a tool which will add N extra redundancy
frames at the end which will allow perfect decoding with up to ~N
frames lost in the files. This would allow users to sacrifice a tiny
amount of compression for a substantial increase in file robustness.

This would also create a new potential audience for Flac: people who
don't care about file size but care substantially about file
robustness. A typical flac bloated back to the original wav size could
lose roughly half its blocks and still remain perfectly decodable.

http://planete-bcast.inrialpes.fr/article.php3?id_article=7 has a nice
high performance error correcting library which would work well for
this sort of application.

--- Gregory Maxwell <gmaxwell@gmail.com> wrote:
> Is there an obvious safe way to add some extra data to a flac file
> that spec decoders will happily ignore?
> 
> I'd like to explore creating a tool which will add N extra redundancy
> frames at the end which will allow perfect decoding with up to ~N
> frames lost in the files. This would allow users to sacrifice a tiny
> amount of compression for a substantial increase in file robustness.
> 
> This would also create a new potential audience for Flac: people who
> don't care about file size but care substantially about file
> robustness. A typical flac bloated back to the original wav size
> could
> lose roughly half its blocks and still remain perfectly decodable.
> 
> http://planete-bcast.inrialpes.fr/article.php3?id_article=7 has a
> nice
> high performance error correcting library which would work well for
> this sort of application.
you could put it in metadata, but error correction data really
belongs in the transport layer because the optimal method of
adding redundancy depends on the characteristics of the
communication channel.

e.g. for CDs a lot of people use quickpar/par2 + FLAC

Josh



 
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