Escient Fireball E-2, Руководство пользователя

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FIREBALL Advanced Users Guide WD041-1-1
10/26/2004
Page 20 of 70
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What is FLAC?
FLAC stands for Free Lossless Audio Codec. Grossly oversimplified, FLAC is similar to MP3,
but lossless, meaning that audio is compressed in FLAC without any loss in quality. This is
similar to how Zip works, except with FLAC you will get much better compression because it is
designed specifically for audio, and you can play back compressed FLAC files just like you
would an MP3 file. The quality of a FLAC encoded file is an exact bit for bit copy of the original
CD audio data. MP3 encoded files are not bit for bit copies of the original audio and therefore
technically don’t equal the quality of the original.
FLAC is freely available and supported on most operating systems, including Windows, "unix"
(Linux, *BSD, Solaris, OS X, IRIX), BeOS, OS/2, Mac OS X, and Amiga.
Notable features of FLAC
x
Lossless: The encoding of audio (PCM) data incurs no loss of information, and the
decoded audio is bit-for-bit identical to what went into the encoder. Each frame contains
a 16-bit CRC of the frame data for detecting transmission errors. The integrity of the
audio data is further insured by storing an MD5 signature of the original unencoded
audio data in the file header, which can be compared against later during decoding or
testing.
x
Fast: FLAC is asymmetric in favor of decode speed. Decoding requires only integer
arithmetic, and is much less compute-intensive than for most perceptual codecs. Real-
time decode performance is easily achievable on even modest hardware.
x Hardware support: Because of FLAC's free reference implementation and low decoding
complexity, FLAC is currently the only lossless codec that has any kind of hardware
support.
x
Streamable: Each FLAC frame contains enough data to decode that frame. FLAC does
not even rely on previous or following frames. FLAC uses sync codes and CRCs
(similar to MPEG and other formats), which, along with framing, allow decoders to pick
up in the middle of a stream with a minimum of delay.
x
Seekable: FLAC supports fast sample-accurate seeking. Not only is this useful for
playback, it makes FLAC files suitable for use in editing applications.
x Flexible metadata: New metadata blocks can be defined and implemented in future
versions of FLAC without breaking older streams or decoders
x
Suitable for archiving: FLAC is an open format, and there is no generation loss if you
need to convert your data to another format in the future. In addition to the frame CRCs
and MD5 signature, flac has a verify option that decodes the encoded stream in parallel
with the encoding process and compares the result to the original, aborting with an error
if there is a mismatch.
x
Convenient CD archiving: FLAC has a "cue sheet" metadata block for storing a CD
table of contents and all track and index points. For instance, you can rip a CD to a
single file, then import the CD's extracted cue sheet while encoding to yield a single file
representation of the entire CD. If your original CD is damaged, the cue sheet can be
exported later in order to burn an exact copy.
x Error resistant: Because of FLAC's framing, stream errors limit the damage to the frame
in which the error occurred, typically a small fraction of a second worth of data. Contrast
this with some other lossless codecs, in which a single error destroys the remainder of
the stream.