flac(1) Free Lossless Audio Codec conversion tool flac(1)
NAME
flac - Free Lossless Audio Codec
SYNOPSIS
flac [ OPTIONS ] [ infile.wav | infile.rf64 | infile.aiff | infile.raw
| infile.flac | infile.oga | infile.ogg | - ... ]
flac [ -d | --decode | -t | --test | -a | --analyze ] [ OPTIONS ] [
infile.flac | infile.oga | infile.ogg | - ... ]
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.
SEE ALSO
flac(1)
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)
flac 1.4.3 - Generated Tue Jul 4 11:25:17 CDT 2023