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.
A summary of options is included below. For a complete
description, see the HTML documentation.
- -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).
- --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.
- --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.
- --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.
- -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 one of 8, 11.025,
12, 16, 22.05, 24, 32, 44.1, or 48 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.
- --sector-align
- Align encoding of multiple CD format files on sector boundaries. See the
HTML documentation for more information. This option is DEPRECATED and may
not exist in future versions of flac.
- --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.
- --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 (the default is signed).
- --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 the decoder to output AIFF format. This option is not needed if the
output filename (as set by -o) ends with .aif or .aiff.
Also, this option has no effect when encoding since input AIFF is
auto-detected.
- --force-rf64-format
- Force the decoder to output RF64 format. This option is not needed if the
output filename (as set by -o) ends with .rf64. Also, this option
has no effect when encoding since input RF64 is auto-detected.
- --force-wave64-format
- Force the decoder to output Wave64 format. This option is not needed if
the output filename (as set by -o) ends with .w64. Also, this
option has no effect when encoding since input Wave64 is
auto-detected.
--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-sector-align
--no-seektable
--no-silent
--no-verify
--no-warnings-as-errors
These flags can be used to invert the sense of the corresponding
normal option.
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:
- •
- preamp: A floating point number in dB. This is added to the
existing gain value.
- •
- 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.
- •
- 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.
- •
- 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.
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.
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.
- •
- For gauss(STDDEV), STDDEV is the standard deviation
(0<STDDEV<=0.5).
- •
- 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”).
- •
- 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.
- •
- 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.