Tribblix: manual page: flac.1

flac(1) Free Lossless Audio Codec conversion tool flac(1)

NAME

flac - Free Lossless Audio Codec

SYNOPSIS

DESCRIPTION

flac is a command-line tool for encoding, decoding, testing and
analyzing FLAC streams.

GENERAL USAGE

flac supports as input RIFF WAVE, Wave64, RF64, AIFF, FLAC or Ogg
FLAC format, or raw interleaved samples. The decoder currently can
output to RIFF WAVE, Wave64, RF64, or AIFF format, or raw interleaved
samples. flac only supports linear PCM samples (in other words, no
A-LAW, uLAW, etc.), and the input must be between 4 and 32 bits per
sample.

flac assumes that files ending in ".wav" or that have the RIFF WAVE
header present are WAVE files, files ending in ".w64" or have the
Wave64 header present are Wave64 files, files ending in ".rf64" or
have the RF64 header present are RF64 files, files ending in ".aif"
or ".aiff" or have the AIFF header present are AIFF files, files
ending in ".flac" or have the FLAC header present are FLAC files and
files ending in ".oga" or ".ogg" or have the Ogg FLAC header present
are Ogg FLAC files.

Other than this, flac makes no assumptions about file extensions,
though the convention is that FLAC files have the extension ".flac"
(or ".fla" on ancient "8.3" file systems like FAT-16).

Before going into the full command-line description, a few other
things help to sort it out: 1. flac encodes by default, so you must
use -d to decode 2. the options -0 .. -8 (or -fast and -best) that
control the compression level actually are just synonyms for
different groups of specific encoding options (described later) and
you can get the same effect by using the same options. When specific
options are specified they take priority over the compression level
no matter the order 3. flac behaves similarly to gzip in the way it
handles input and output files 4. the order in which options are
specified is generally not important

Skip to the examples below for examples of some common tasks.

flac will be invoked one of four ways, depending on whether you are
encoding, decoding, testing, or analyzing. Encoding is the default
invocation, but can be switch to decoding with -d, analysis with -a
or testing with -t. Depending on which way is chosen, encoding,
decoding, analysis or testing options can be used, see section
OPTIONS for details. General options can be used for all.

If only one inputfile is specified, it may be "-" for stdin. When
stdin is used as input, flac will write to stdout. Otherwise flac
will perform the desired operation on each input file to similarly
named output files (meaning for encoding, the extension will be
replaced with ".flac", or appended with ".flac" if the input file has
no extension, and for decoding, the extension will be ".wav" for WAVE
output and ".raw" for raw output). The original file is not deleted
unless -delete-input-file is specified.

If you are encoding/decoding from stdin to a file, you should use the
-o option like so:

flac [options] -o outputfile
flac -d [options] -o outputfile

which are better than:

flac [options] > outputfile
flac -d [options] > outputfile

since the former allows flac to seek backwards to write the
STREAMINFO or RIFF WAVE header contents when necessary.

Also, you can force output data to go to stdout using -c.

To encode or decode files that start with a dash, use - to signal the
end of options, to keep the filenames themselves from being treated
as options:

flac -V -- -01-filename.wav

The encoding options affect the compression ratio and encoding speed.
The format options are used to tell flac the arrangement of samples
if the input file (or output file when decoding) is a raw file. If
it is a RIFF WAVE, Wave64, RF64, or AIFF file the format options are
not needed since they are read from the file's header.

In test mode, flac acts just like in decode mode, except no output
file is written. Both decode and test modes detect errors in the
stream, but they also detect when the MD5 signature of the decoded
audio does not match the stored MD5 signature, even when the
bitstream is valid.

flac can also re-encode FLAC files. In other words, you can specify
a FLAC or Ogg FLAC file as an input to the encoder and it will
decoder it and re-encode it according to the options you specify. It
will also preserve all the metadata unless you override it with other
options (e.g. specifying new tags, seekpoints, cuesheet, padding,
etc.).

flac has been tuned so that the default settings yield a good speed
vs. compression tradeoff for many kinds of input. However, if you
are looking to maximize the compression rate or speed, or want to use
the full power of FLAC's metadata system, see the page titled `About
the FLAC Format' on the FLAC website.

EXAMPLES

Some common encoding tasks using flac:

flac abc.wav
Encode abc.wav to abc.flac using the default compression
setting. abc.wav is not deleted.

flac --delete-input-file abc.wav
Like above, except abc.wav is deleted if there were no errors.

flac --delete-input-file -w abc.wav
Like above, except abc.wav is deleted if there were no errors
or warnings.

flac --best abc.wav
Encode abc.wav to abc.flac using the highest compression
setting.

flac --verify abc.wav
Encode abc.wav to abc.flac and internally decode abc.flac to
make sure it matches abc.wav.

flac -o my.flac abc.wav
Encode abc.wav to my.flac.

flac -T "TITLE=Bohemian Rhapsody" -T "ARTIST=Queen" abc.wav
Encode abc.wav and add some tags at the same time to abc.flac.

flac *.wav
Encode all .wav files in the current directory.

flac abc.aiff
Encode abc.aiff to abc.flac.

flac abc.rf64
Encode abc.rf64 to abc.flac.

flac abc.w64
Encode abc.w64 to abc.flac.

flac abc.flac --force
This one's a little tricky: notice that flac is in encode mode
by default (you have to specify -d to decode) so this command
actually recompresses abc.flac back to abc.flac. -force is
needed to make sure you really want to overwrite abc.flac with
a new version. Why would you want to do this? It allows you
to recompress an existing FLAC file with (usually) higher
compression options or a newer version of FLAC and preserve
all the metadata like tags too.

Some common decoding tasks using flac:

flac -d abc.flac
Decode abc.flac to abc.wav. abc.flac is not deleted. NOTE:
Without -d it means re-encode abc.flac to abc.flac (see
above).

flac -d --force-aiff-format abc.flac
flac -d -o abc.aiff abc.flac : Two different ways of decoding
abc.flac to abc.aiff (AIFF format). abc.flac is not deleted.

flac -d --force-rf64-format abc.flac
flac -d -o abc.rf64 abc.flac : Two different ways of decoding
abc.flac to abc.rf64 (RF64 format). abc.flac is not deleted.

flac -d --force-wave64-format abc.flac
flac -d -o abc.w64 abc.flac : Two different ways of decoding abc.flac
to abc.w64 (Wave64 format). abc.flac is not deleted.

flac -d -F abc.flac
Decode abc.flac to abc.wav and don't abort if errors are found
(useful for recovering as much as possible from corrupted
files).

OPTIONS

A summary of options is included below. For a complete description,
see the HTML documentation.

GENERAL OPTIONS

-v, --version
Show the flac version number

-h, --help
Show basic usage and a list of all options

-H, --explain
Show detailed explanation of usage and all options

-d, --decode
Decode (the default behavior is to encode)

-t, --test
Test a flac encoded file (same as -d except no decoded file is
written)

-a, --analyze
Analyze a FLAC encoded file (same as -d except an analysis
file is written)

-c, --stdout
Write output to stdout

-s, --silent
Silent mode (do not write runtime encode/decode statistics to
stderr)

--totally-silent
Do not print anything of any kind, including warnings or
errors. The exit code will be the only way to determine
successful completion.

--no-utf8-convert
Do not convert tags from local charset to UTF-8. This is
useful for scripts, and setting tags in situations where the
locale is wrong. This option must appear before any tag
options!

-w, --warnings-as-errors
Treat all warnings as errors (which cause flac to terminate
with a non-zero exit code).

-f, --force
Force overwriting of output files. By default, flac warns
that the output file already exists and continues to the next
file.

-o filename, --output-name=filename
Force the output file name (usually flac just changes the
extension). May only be used when encoding a single file.
May not be used in conjunction with --output-prefix.

--output-prefix=string
Prefix each output file name with the given string. This can
be useful for encoding or decoding files to a different
directory. Make sure if your string is a path name that it
ends with a trailing `/' (slash).

--delete-input-file
Automatically delete the input file after a successful encode
or decode. If there was an error (including a verify error)
the input file is left intact.

--preserve-modtime
Output files have their timestamps/permissions set to match
those of their inputs (this is default). Use --no-preserve-
modtime to make output files have the current time and default
permissions.

--keep-foreign-metadata
If encoding, save WAVE, RF64, or AIFF non-audio chunks in FLAC
metadata. If decoding, restore any saved non-audio chunks
from FLAC metadata when writing the decoded file. Foreign
metadata cannot be transcoded, e.g. WAVE chunks saved in a
FLAC file cannot be restored when decoding to AIFF. Input and
output must be regular files (not stdin or stdout). With this
option, FLAC will pick the right output format on decoding.

--keep-foreign-metadata-if-present
Like --keep-foreign-metadata, but without throwing an error if
foreign metadata cannot be found or restored, instead printing
a warning.

--skip={#|mm:ss.ss}
Skip over the first number of samples of the input. This
works for both encoding and decoding, but not testing. The
alternative form mm:ss.ss can be used to specify minutes,
seconds, and fractions of a second.

--until={#|[+|-]mm:ss.ss}
Stop at the given sample number for each input file. This
works for both encoding and decoding, but not testing. The
given sample number is not included in the decoded output.
The alternative form mm:ss.ss can be used to specify minutes,
seconds, and fractions of a second. If a `+' (plus) sign is
at the beginning, the --until point is relative to the --skip
point. If a `-' (minus) sign is at the beginning, the --until
point is relative to end of the audio.

--ogg When encoding, generate Ogg FLAC output instead of native
FLAC. Ogg FLAC streams are FLAC streams wrapped in an Ogg
transport layer. The resulting file should have an `.oga'
extension and will still be decodable by flac. When decoding,
force the input to be treated as Ogg FLAC. This is useful
when piping input from stdin or when the filename does not end
in `.oga' or `.ogg'.

--serial-number=#
When used with --ogg, specifies the serial number to use for
the first Ogg FLAC stream, which is then incremented for each
additional stream. When encoding and no serial number is
given, flac uses a random number for the first stream, then
increments it for each additional stream. When decoding and
no number is given, flac uses the serial number of the first
page.

ANALYSIS OPTIONS

--residual-text
Includes the residual signal in the analysis file. This will
make the file very big, much larger than even the decoded
file.

--residual-gnuplot
Generates a gnuplot file for every subframe; each file will
contain the residual distribution of the subframe. This will
create a lot of files.

DECODING OPTIONS

--cue=[#.#][-[#.#]]
Set the beginning and ending cuepoints to decode. The
optional first #.# is the track and index point at which
decoding will start; the default is the beginning of the
stream. The optional second #.# is the track and index point
at which decoding will end; the default is the end of the
stream. If the cuepoint does not exist, the closest one
before it (for the start point) or after it (for the end
point) will be used. If those don't exist, the start of the
stream (for the start point) or end of the stream (for the end
point) will be used. The cuepoints are merely translated into
sample numbers then used as --skip and --until. A CD track
can always be cued by, for example, --cue=9.1-10.1 for track
9, even if the CD has no 10th track.

-F, --decode-through-errors
By default flac stops decoding with an error and removes the
partially decoded file if it encounters a bitstream error.
With -F, errors are still printed but flac will continue
decoding to completion. Note that errors may cause the
decoded audio to be missing some samples or have silent
sections.

--apply-replaygain-which-is-not-lossless[=<specification>]
Applies ReplayGain values while decoding. WARNING: THIS IS
NOT LOSSLESS. DECODED AUDIO WILL NOT BE IDENTICAL TO THE
ORIGINAL WITH THIS OPTION. This option is useful for example
in transcoding media servers, where the client does not
support ReplayGain. For details on the use of this option,
see the section ReplayGain application specification.

ENCODING OPTIONS

-V, --verify
Verify a correct encoding by decoding the output in parallel
and comparing to the original

--lax Allow encoder to generate non-Subset files. The resulting
FLAC file may not be streamable or might have trouble being
played in all players (especially hardware devices), so you
should only use this option in combination with custom
encoding options meant for archival.

--replay-gain
Calculate ReplayGain values and store them as FLAC tags,
similar to vorbisgain. Title gains/peaks will be computed for
each input file, and an album gain/peak will be computed for
all files. All input files must have the same resolution,
sample rate, and number of channels. Only mono and stereo
files are allowed, and the sample rate must be 8, 11.025, 12,
16, 18.9, 22.05, 24, 28, 32, 36, 37.8, 44.1, 48, 56, 64, 72,
75.6, 88.2, 96, 112, 128, 144, 151.2, 176.4, 192, 224, 256,
288, 302.4, 352.8, 384, 448, 512, 576, or 604.8 kHz. Also
note that this option may leave a few extra bytes in a PADDING
block as the exact size of the tags is not known until all
files are processed. Note that this option cannot be used
when encoding to standard output (stdout).

--cuesheet=filename
Import the given cuesheet file and store it in a CUESHEET
metadata block. This option may only be used when encoding a
single file. A seekpoint will be added for each index point
in the cuesheet to the SEEKTABLE unless --no-cued-seekpoints
is specified.

--picture={FILENAME|SPECIFICATION}
Import a picture and store it in a PICTURE metadata block.
More than one --picture option can be specified. Either a
filename for the picture file or a more complete specification
form can be used. The SPECIFICATION is a string whose parts
are separated by | (pipe) characters. Some parts may be left
empty to invoke default values. FILENAME is just shorthand
for "||||FILENAME". For the format of SPECIFICATION, see the
section picture specification.

--ignore-chunk-sizes
When encoding to flac, ignore the file size headers in WAV and
AIFF files to attempt to work around problems with over-sized
or malformed files. WAV and AIFF files both have an unsigned
32 bit numbers in the file header which specifes the length of
audio data. Since this number is unsigned 32 bits, that
limits the size of a valid file to being just over 4
Gigabytes. Files larger than this are mal-formed, but should
be read correctly using this option.

-S {#|X|#x|#s}, --seekpoint={#|X|#x|#s}
Include a point or points in a SEEKTABLE. Using #, a seek
point at that sample number is added. Using X, a placeholder
point is added at the end of a the table. Using #x, # evenly
spaced seek points will be added, the first being at sample 0.
Using #s, a seekpoint will be added every # seconds (# does
not have to be a whole number; it can be, for example, 9.5,
meaning a seekpoint every 9.5 seconds). You may use many -S
options; the resulting SEEKTABLE will be the unique-ified
union of all such values. With no -S options, flac defaults
to `-S 10s'. Use --no-seektable for no SEEKTABLE. Note: `-S
#x' and `-S #s' will not work if the encoder can't determine
the input size before starting. Note: if you use `-S #' and #
is >= samples in the input, there will be either no seek point
entered (if the input size is determinable before encoding
starts) or a placeholder point (if input size is not
determinable).

-P #, --padding=#
Tell the encoder to write a PADDING metadata block of the
given length (in bytes) after the STREAMINFO block. This is
useful if you plan to tag the file later with an APPLICATION
block; instead of having to rewrite the entire file later just
to insert your block, you can write directly over the PADDING
block. Note that the total length of the PADDING block will
be 4 bytes longer than the length given because of the 4
metadata block header bytes. You can force no PADDING block
at all to be written with --no-padding. The encoder writes a
PADDING block of 8192 bytes by default (or 65536 bytes if the
input audio stream is more that 20 minutes long).

-T FIELD=VALUE, --tag=FIELD=VALUE
Add a FLAC tag. The comment must adhere to the Vorbis comment
spec; i.e. the FIELD must contain only legal characters,
terminated by an `equals' sign. Make sure to quote the
comment if necessary. This option may appear more than once
to add several comments. NOTE: all tags will be added to all
encoded files.

--tag-from-file=FIELD=FILENAME
Like --tag, except FILENAME is a file whose contents will be
read verbatim to set the tag value. The contents will be
converted to UTF-8 from the local charset. This can be used
to store a cuesheet in a tag (e.g. --tag-from-
file="CUESHEET=image.cue"). Do not try to store binary data
in tag fields! Use APPLICATION blocks for that.

-b #, --blocksize=#
Specify the blocksize in samples. The default is 1152 for -l
0, else 4096. For subset streams this must be <= 4608 if the
samplerate <= 48kHz, for subset streams with higher
samplerates it must be <= 16384.

-m, --mid-side
Try mid-side coding for each frame (stereo input only)

-M, --adaptive-mid-side
Adaptive mid-side coding for all frames (stereo input only)

-0..-8, --compression-level-0..--compression-level-8
Fastest compression..highest compression (default is -5).
These are synonyms for other options:

-0, --compression-level-0
Synonymous with -l 0 -b 1152 -r 3 --no-mid-side

-1, --compression-level-1
Synonymous with -l 0 -b 1152 -M -r 3

-2, --compression-level-2
Synonymous with -l 0 -b 1152 -m -r 3

-3, --compression-level-3
Synonymous with -l 6 -b 4096 -r 4 --no-mid-side

-4, --compression-level-4
Synonymous with -l 8 -b 4096 -M -r 4

-5, --compression-level-5
Synonymous with -l 8 -b 4096 -m -r 5

-6, --compression-level-6
Synonymous with -l 8 -b 4096 -m -r 6 -A subdivide_tukey(2)

-7, --compression-level-7
Synonymous with -l 12 -b 4096 -m -r 6 -A subdivide_tukey(2)

-8, --compression-level-8
Synonymous with -l 12 -b 4096 -m -r 6 -A subdivide_tukey(3)

--fast Fastest compression. Currently synonymous with -0.

--best Highest compression. Currently synonymous with -8.

-e, --exhaustive-model-search
Do exhaustive model search (expensive!)

-A function, --apodization=function
Window audio data with given the apodization function. See
section Apodization functions for details.

-l #, --max-lpc-order=#
Specifies the maximum LPC order. This number must be <= 32.
For subset streams, it must be <=12 if the sample rate is
<=48kHz. If 0, the encoder will not attempt generic linear
prediction, and use only fixed predictors. Using fixed
predictors is faster but usually results in files being 5-10%
larger.

-p, --qlp-coeff-precision-search
Do exhaustive search of LP coefficient quantization
(expensive!). Overrides -q; does nothing if using -l 0

-q #, --qlp-coeff-precision=#
Precision of the quantized linear-predictor coefficients, 0 =>
let encoder decide (min is 5, default is 0)

-r [#,]#, --rice-partition-order=[#,]#
Set the [min,]max residual partition order (0..15). min
defaults to 0 if unspecified. Default is -r 5.

FORMAT OPTIONS

--endian={big|little}
Set the byte order for samples

--channels=#
Set number of channels.

--bps=#
Set bits per sample.

--sample-rate=#
Set sample rate (in Hz).

--sign={signed|unsigned}
Set the sign of samples.

--input-size=#
Specify the size of the raw input in bytes. If you are
encoding raw samples from stdin, you must set this option in
order to be able to use --skip, --until, --cuesheet, or other
options that need to know the size of the input beforehand.
If the size given is greater than what is found in the input
stream, the encoder will complain about an unexpected end-of-
file. If the size given is less, samples will be truncated.

--force-raw-format
Force input (when encoding) or output (when decoding) to be
treated as raw samples (even if filename ends in .wav).

--force-aiff-format
--force-rf64-format
--force-wave64-format : Force the decoder to output AIFF/RF64/WAVE64
format respectively. This option is not needed if the output
filename (as set by -o) ends with .aif or .aiff, .rf64 and .w64
respectively. Also, this option has no effect when encoding since
input is auto-detected. When none of these options nor -keep-
foreign-metadata are given and no output filename is set, the output
format is WAV by default.

--force-legacy-wave-format
--force-extensible-wave-format : Instruct the decoder to output a
WAVE file with WAVE_FORMAT_PCM and WAVE_FORMAT_EXTENSIBLE
respectively. If none of these options nor -keep-foreign-metadata
are given, FLAC outputs WAVE_FORMAT_PCM for mono or stereo with a bit
depth of 8 or 16 bits, and WAVE_FORMAT_EXTENSIBLE for all other audio
formats.

--force-aiff-c-none-format
--force-aiff-c-sowt-format : Instruct the decoder to output an AIFF-C
file with format NONE and sowt respectively.

NEGATIVE OPTIONS

--no-adaptive-mid-side
--no-cued-seekpoints
--no-decode-through-errors
--no-delete-input-file
--no-preserve-modtime
--no-keep-foreign-metadata
--no-exhaustive-model-search
--no-force
--no-lax
--no-mid-side
--no-ogg
--no-padding
--no-qlp-coeff-prec-search
--no-replay-gain
--no-residual-gnuplot
--no-residual-text
--no-seektable
--no-silent
--no-verify
--no-warnings-as-errors

These flags can be used to invert the sense of the corresponding
normal option.

ReplayGain application specification

The option --apply-replaygain-which-is-not-lossless[=<specification>]
applies ReplayGain values while decoding. WARNING: THIS IS NOT
LOSSLESS. DECODED AUDIO WILL NOT BE IDENTICAL TO THE ORIGINAL WITH
THIS OPTION.** This option is useful for example in transcoding media
servers, where the client does not support ReplayGain.

The equals sign and <specification> is optional. If omitted, the
default specification is 0aLn1.

The <specification> is a shorthand notation for describing how to
apply ReplayGain. All components are optional but order is
important. `[]' means `optional'. `|' means `or'. `{}' means
required. The format is:

[<preamp>][a|t][l|L][n{0|1|2|3}]

In which the following parameters are used:

+o preamp: A floating point number in dB. This is added to the
existing gain value.

+o a|t: Specify `a' to use the album gain, or `t' to use the track
gain. If tags for the preferred kind (album/track) do not exist
but tags for the other (track/album) do, those will be used
instead.

+o l|L: Specify `l' to peak-limit the output, so that the ReplayGain
peak value is full-scale. Specify `L' to use a 6dB hard limiter
that kicks in when the signal approaches full-scale.

+o n{0|1|2|3}: Specify the amount of noise shaping. ReplayGain
synthesis happens in floating point; the result is dithered before
converting back to integer. This quantization adds noise. Noise
shaping tries to move the noise where you won't hear it as much. 0
means no noise shaping, 1 means `low', 2 means `medium', 3 means
`high'.

For example, the default of 0aLn1 means 0dB preamp, use album gain,
6dB hard limit, low noise shaping. --apply-replaygain-which-is-not-
lossless=3 means 3dB preamp, use album gain, no limiting, no noise
shaping.

flac uses the ReplayGain tags for the calculation. If a stream does
not have the required tags or they can't be parsed, decoding will
continue with a warning, and no ReplayGain is applied to that stream.

Picture specification

This described the specification used for the --picture option.
[TYPE]|[MIME-TYPE]|[DESCRIPTION]|[WIDTHxHEIGHTxDEPTH[/COLORS]]|FILE

TYPE is optional; it is a number from one of:

0. Other

1. 32x32 pixels `file icon' (PNG only)

2. Other file icon

3. Cover (front)

4. Cover (back)

5. Leaflet page

6. Media (e.g. label side of CD)

7. Lead artist/lead performer/soloist

8. Artist/performer

9. Conductor

10. Band/Orchestra

11. Composer

12. Lyricist/text writer

13. Recording Location

14. During recording

15. During performance

16. Movie/video screen capture

17. A bright coloured fish

18. Illustration

19. Band/artist logotype

20. Publisher/Studio logotype

The default is 3 (front cover). There may only be one picture each
of type 1 and 2 in a file.

MIME-TYPE is optional; if left blank, it will be detected from the
file. For best compatibility with players, use pictures with MIME
type image/jpeg or image/png. The MIME type can also be --> to mean
that FILE is actually a URL to an image, though this use is
discouraged.

DESCRIPTION is optional; the default is an empty string.

The next part specifies the resolution and color information. If the
MIME-TYPE is image/jpeg, image/png, or image/gif, you can usually
leave this empty and they can be detected from the file. Otherwise,
you must specify the width in pixels, height in pixels, and color
depth in bits-per-pixel. If the image has indexed colors you should
also specify the number of colors used. When manually specified, it
is not checked against the file for accuracy.

FILE is the path to the picture file to be imported, or the URL if
MIME type is -->

For example, "|image/jpeg|||../cover.jpg" will embed the JPEG file at
../cover.jpg, defaulting to type 3 (front cover) and an empty
description. The resolution and color info will be retrieved from
the file itself.

The specification
"4|-->|CD|320x300x24/173|http://blah.blah/backcover.tiff" will embed
the given URL, with type 4 (back cover), description "CD", and a
manually specified resolution of 320x300, 24 bits-per-pixel, and 173
colors. The file at the URL will not be fetched; the URL itself is
stored in the PICTURE metadata block.

Apodization functions

To improve LPC analysis, audio data is windowed . The window can be
selected with one or more -A options. Possible functions are:
bartlett, bartlett_hann, blackman, blackman_harris_4term_92db,
connes, flattop, gauss(STDDEV), hamming, hann, kaiser_bessel,
nuttall, rectangle, triangle, tukey(P), partial_tukey(n[/ov[/P]]),
punchout_tukey(n[/ov[/P]]), subdivide_tukey(n[/P]) welch.

+o For gauss(STDDEV), STDDEV is the standard deviation
(0<STDDEV<=0.5).

+o For tukey(P), P specifies the fraction of the window that is
tapered (0<=P<=1; P=0 corresponds to "rectangle" and P=1
corresponds to "hann").

+o For partial_tukey(n) and punchout_tukey(n), n apodization functions
are added that span different parts of each block. Values of 2 to
6 seem to yield sane results. If necessary, an overlap can be
specified, as can be the taper parameter, for example
partial_tukey(2/0.2) or partial_tukey(2/0.2/0.5). ov should be
smaller than 1 and can be negative. The use of this is that
different parts of a block are ignored as the might contain
transients which are hard to predict anyway. The encoder will try
each different added apodization (each covering a different part of
the block) to see which resulting predictor results in the smallest
representation.

+o subdivide_tukey(n) is a more efficient reimplementation of
partial_tukey and punchout_tukey taken together, recycling as much
data as possible. It combines all possible non-redundant
partial_tukey(n) and punchout_tukey(n) up to the n specified.
Specifying subdivide_tukey(3) is equivalent to specifying tukey,
partial_tukey(2), partial_tukey(3) and punchout_tukey(3),
specifying subdivide_tukey(5) equivalently adds partial_tukey(4),
punchout_tukey(4), partial_tukey(5) and punchout_tukey(5). To be
able to reuse data as much as possible, the tukey taper is taken
equal for all windows, and the P specified is applied for the
smallest used window. In other words, subdivide_tukey(2/0.5)
results in a taper equal to that of tukey(0.25) and
subdivide_tukey(5) in a taper equal to that of tukey(0.1). The
default P for subdivide_tukey when none is specified is 0.5.

Note that P, STDDEV and ov are locale specific, so a comma as decimal
separator might be required instead of a dot. Use scientific
notation for a locale-independent specification, for example
tukey(5e-1) instead of tukey(0.5) or tukey(0,5).

More than one -A option (up to 32) may be used. Any function that is
specified erroneously is silently dropped. The encoder chooses
suitable defaults in the absence of any -A options; any -A option
specified replaces the default(s).

When more than one function is specified, then for every subframe the
encoder will try each of them separately and choose the window that
results in the smallest compressed subframe. Multiple functions can
greatly increase the encoding time.

AUTHOR

This manual page was initially written by Matt Zimmerman
<mdz@debian.org> for the Debian GNU/Linux system (but may be used by
others). It has been kept up-to-date by the Xiph.org Foundation.

Version 1.4.3 flac(1)