[FFmpeg-devel] [PATCH] handle INT32INFO in WavPack decoder

[Michael Niedermayer]

Hi

On Sat, Aug 04, 2007 at 10:06:53PM -0700, David Bryant wrote:
[...]
>>> but is also used with smaller integers to efficiently encode audio blocks 
>>> that have redundancies in their LSBs (e.g. all zeros, all ones, etc.)
>> etc == duplicate some bit into all LSBs
>> the upscaling by adding 0 bits i can still understand but the other cases?
>> this seems like a senseless misdesign
>> is this used by any real files in the wild? if no then iam against 
>> supporting
>> it
>> if it is we dont have a choice but its ugly, the format could as well 
>> contain
>> a special case to store 0xDEADBEAF in the lsbs more efficiently
>
> The 0 bit case is the most common, but I have certainly encountered the 
> other two cases. One specific case I remember was Adobe Audition generating 
> 32-bit integer files from 24-bit sources that had the LSB filled in with 
> sometimes 0s and sometimes 1s, obviously from dithering when it should not 
> have.
>
> As an aside, I have certainly been surprised by some of the weird audio 
> data I've seen on CDs. Some audio production software obviously does 
> undithered normalization and ends up creating CDs with missing sample 
> values in regular patterns. I even saw a track where every sample was a 
> multiple of 3!
>
> Regular lossless audio compression algorithms do not detect these cases 
> because the decorrelation destroys the patterns, but early on I considered 
> adding detection and handling of [some of] these cases to WavPack but 
> decided in the end that it was too ugly (even though it could sometimes 
> make a significant improvement in compression).

well if your goal is to losslessly compress "lossy"/"misfiltered" audio
then such special cases would make sense though trying to losslessly
compress these seems to not make that much sense to begin with ...

that is just setting these LBSs to zero might very well be closer to
the original untrashed audio ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
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