Flac - Nov 2005 - Exact metadata reproduction

Hi!  I'm just now preparing the first, still very experimental (way pre-1.0)
release of a new archival tool, similar to (and based on) zip/unzip, with the 
difference that the enhanced zip tool can store x86-based decompressor code 
fragments in archives along with the compressed data, which the unzip tool 
runs in an isolated user-mode virtual machine in order to extract the data.  
The main benefit is that the archiver can upgrade or adapt its compression 
algorithms to different file types without further changing the basic archive 
format or breaking compatibility with existing tools.  The new tools and the 
virtual machine they are based on are more fully described in this paper (to 
appear in USENIX File and Storage Technologies next month):

	http://www.brynosaurus.com/pub/os/vxa.pdf
	http://www.brynosaurus.com/pub/os/vxa/ (HTML version)

I've already integrated FLAC as an example media-type-specific compressor
that
the archiver can use automatically on WAV files it runs across, rather than 
futilely trying to run them through gzip or another general-purpose 
algorithm.  It works, and everything's peachy, except for the minor problem 
that FLAC is currently only lossless at the audio data level and not at the 
file level.  I see that this issue has already been discussed on this list 
and is in the FAQ, and for the current typical uses of FLAC I don't see its 
current behavior as a problem.  But to work as a component of a 
general-purpose archiver that's supposed to (by default anyway) reproduce
the
files it archives _exactly_, we really need exact metadata replication for 
whatever uncompressed audio formats it supports (certainly WAV, ideally 8SVX 
too).

So, my question: has anyone done work on adding exact metadata replication 
support to FLAC, or is it currently planned or on the horizon?

Thanks!
Bryan

--- Bryan Ford <baford@mit.edu> wrote:
[...]
> 	http://www.brynosaurus.com/pub/os/vxa.pdf
ooh, very cool.
> I've already integrated FLAC as an example media-type-specific
> compressor that 
> the archiver can use automatically on WAV files it runs across,
> rather than 
> futilely trying to run them through gzip or another general-purpose 
> algorithm.  It works, and everything's peachy, except for the minor
> problem 
> that FLAC is currently only lossless at the audio data level and not
> at the 
> file level.  I see that this issue has already been discussed on this
> list 
> and is in the FAQ, and for the current typical uses of FLAC I don't
> see its 
> current behavior as a problem.  But to work as a component of a 
> general-purpose archiver that's supposed to (by default anyway)
> reproduce the 
> files it archives _exactly_, we really need exact metadata
> replication for 
> whatever uncompressed audio formats it supports (certainly WAV,
> ideally 8SVX 
> too).
> 
> So, my question: has anyone done work on adding exact metadata
> replication 
> support to FLAC, or is it currently planned or on the horizon?
no, that's really outside the design goals of FLAC,
it will probably never be a WAVE file compressor.

but, for vxa you could develop a 'super-WAVE' format
for handling WAVE which on the encoder side splits a
WAVE file logically like so:

[RIFFWAVE.......]['data' subchunk][.....]

then uses a generic compressor to store the prefix
and suffix, and use libFLAC to compress the audio.

there are some other formats that are just WAVE
compressors, and these would solve the problem for
WAVE too but, you would still need a similar
super-AIFF format for AIFF, and so on, since there
are no such general compressors for those that I
know of.

so a general super-format system could be of wider
use.

as a hack, when dealing with 16-bit mono/stereo WAVEs,
you can feed the whole stream file to libFLAC as raw
samples and it will do almost as well.  this will
actually work for any file where the sample data is
aligned (e.g. 8 bit but probably not 20/24 bit).  e.g.
for a WAVE ripped from CD try:

flac --force-raw-format --endian=little --sign=signed
  --channels=2 --bps=16 --sample-rate=44100 file.wav

Josh



	
		
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