[flac-dev] Looking for users of --keep-foreign-metadata

[Federico Miyara]

Martijn,

> Currently FLAC already stores and restores most kinds of metadata 
> corruption without problems, so in most cases the conversion is 
> already bit-accurate. However, there are some kinds of corruption it 
> cannot handle. These are the kinds of corruption that invalidate your 
> considerations. For example, when a chunk length is incorrect, the 
> location and length of the audio data is no longer known. It is also 
> possible the basic formatting information is invalid. In this case, 
> FLAC cannot compress the audio at all, not even without considering 
> foreign metadata, while general purpose compressors (who don't have to 
> discriminate between audio and metadata) have no problem compressing.

OK.

That's why I said

"as long as the audio data is consistent, with known format and 
correctly located."

However, I think there are relatively few uncompressed formats, and 
probably all of them share having large audio blocks. It would be 
feasible to think of an algorithm that attempts to find audio alignment 
by iteratively testing a short portion for different alignments (meaning 
different number of channels and bit depths, little/big endianness, and 
a few other variants or combinations of PCM) until the maximum 
compression is attained. Once located the optimum alignment, the FLAC 
algorithm would provide bit-for-bit accuracy and maximum compression, 
even in the absence of format-awareness. It would take a bit more time 
to encode and could generate its internal header for direct playback 
compatibility.

Regards,

Federico Miyara



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