lame.1

mp3编码源代码

During the development of version 3.90,
considerable tuning was done on this algorithm,
and it is now considered to be on par with the original
.B \-\-vbr-old. 
It has the added advantage of being very fast (over twice as fast as
.B \-\-vbr-old).
.TP
.BI -V " n"
0 <=
.I n
<= 9
.br
Enable VBR (Variable BitRate) and specifies the value of VBR quality
(default = 4).
0 = highest quality.

.PP
ABR and VBR options:
.TP
.BI -b " bitrate"
For MPEG1 (sampling frequencies of 32, 44.1 and 48 kHz)
.br
.I n
= 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320

For MPEG2 (sampling frequencies of 16, 22.05 and 24 kHz)
.br
.I n
= 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160

Specifies the minimum bitrate to be used.
However,
in order to avoid wasted space,
the smallest frame size available will be used during silences. 
.TP
.BI -B " bitrate"
For MPEG1 (sampling frequencies of 32, 44.1 and 48 kHz)
.br
.I n
= 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320

For MPEG2 (sampling frequencies of 16, 22.05 and 24 kHz)
.br
.I n
= 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160

Specifies the maximum allowed bitrate.

Note: If you own an mp3 hardware player build upon a MAS 3503 chip,
you must set maximum bitrate to no more than 224 kpbs. 
.TP
.B -F
Strictly enforce the
.B -b
option.
.br
This is mainly for use with hardware players that do not support low
bitrate mp3.

Without this option,
the minimum bitrate will be ignored for passages of analog silence,
i.e. when the music level is below the absolute threshold of
human hearing (ATH). 

.PP
ATH related:
.TP
.B \-\-noath
Disable any use of the ATH (absolute threshold of hearing) for masking.
Normally,
humans are unable to hear any sound below this threshold. 
.TP
.B \-\-athshort
Ignore psychoacoustic model for short blocks,
use ATH only. 
.TP
.B \-\-athonly
This option causes LAME to ignore the output of the psy-model and only
use masking from the ATH (absolute threshold of hearing).
Might be useful at very high bitrates or for testing the ATH. 
.TP
.BI \-\-athtype " shape"
The Absolute Threshold of Hearing is the minimum threshold under which
humans are unable to hear any sound.
.br
In the past,
LAME was using ATH shape 0 which is the Painter & Spanias formula.
Tests have shown that this formula is innacurate for the
13 - 22 kHz area,
leading to audible artifacts in some cases.
.br
Shape 1 was thus implemented,
which is over sensitive,
leading to very high bitrates.
.br
Shape 2 formula was accurately modelized from real data in order to
reach optimal quality while not wasting bitrate.
In CBR and ABR modes,
LAME uses ATH shape 2 by default,
VBR selects one depending on the specified parameter to the
.B -V
option.
.TP
.BI \-\-athlower " n"
Lower the ATH (absolute threshold of hearing) by
.I n
dB.
.br
Normally,
humans are unable to hear any sound below this threshold,
but for music recorded at very low level this option might be useful.
.TP
.BI \-\-athaa-type " n"
ATH auto adjust types 1 - 3,
else no adjustment
.TP
.BI \-\-athaa-sensitivity " x"
activation offset in -/+ dB for ATH auto-adjustment

.PP
PSY related:
.TP
.B \-\-short
Let LAME use short blocks when appropriate.
It is the default setting.
.TP
.B \-\-noshort
Encode all frames using long blocks only.
This could increase quality when encoding at very low bitrates,
but can produce serious pre-echo artefacts. 
.TP
.B \-\-allshort
Use only short blocks,
no long ones. 
.TP
.BI \-\-cwlimit " freq"
Compute tonality up to
.I freq
(in kHz).
Default setting is 8.8717.
.TP
.B \-\-notemp
Do not make use of the temporal masking effect. 
.TP
.B \-\-nspsytune
Experimental PSY tunings by Naoki Shibata
.TP
.B \-\-nssafejoint
M/S switching criterion
.TP
.BI \-\-nsmsfix " arg"
M/S switching tuning [effective 0-3.5]
.TP
.BI \-\-ns-bass " x"
Adjust masking for sfbs  0 -  6 (long)  0 -  5 (short)
.TP
.BI \-\-ns-alto " x"
Adjust masking for sfbs  7 - 13 (long)  6 - 10 (short)
.TP
.BI \-\-ns-treble " x"
Adjust masking for sfbs 14 - 21 (long) 11 - 12 (short)
.TP
.BI \-\-ns-sfb21 " x"
Change ns-treble by x dB for sfb21

.PP
Experimental options:
.TP
.BI -X " n"
0 <=
.I n
<= 7

When LAME searches for a "good" quantization,
it has to compare the actual one with the best one found so far. 
The comparison says which one is better,
the best so far or the actual.
The
.B -X
parameter selects between different approaches to make this decision,
.B -X0
being the default mode:

.B -X0 
.br
The criterions are (in order of importance):
.br
* less distorted scalefactor bands
.br
* the sum of noise over the thresholds is lower
.br
* the total noise is lower

.B -X1
.br
The actual is better if the maximum noise over all scalefactor bands is
less than the best so far.

.B -X2
.br
The actual is better if the total sum of noise is lower than the best so
far.

.B -X3
.br
The actual is better if the total sum of noise is lower than the best so
far and the maximum noise over all scalefactor bands is less than the
best so far plus 2dB.

.B -X4
.br
Not yet documented.

.B -X5
.br
The criterions are (in order of importance):
.br
* the sum of noise over the thresholds is lower 
.br
* the total sum of noise is lower

.B -X6 
.br
The criterions are (in order of importance):
.br
* the sum of noise over the thresholds is lower
.br
* the maximum noise over all scalefactor bands is lower
.br
* the total sum of noise is lower

.B -X7 
.br
The criterions are:
.br
* less distorted scalefactor bands
.br
or
.br
* the sum of noise over the thresholds is lower 
.TP
.B -Y
lets LAME ignore noise in sfb21, like in CBR
.TP
.B -Z
toggles the scalefac feature on

.PP
MP3 header/stream options:
.TP
.BI -e " emp"
.I emp
= n, 5, c

n = (none, default)
.br
5 = 0/15 microseconds
.br
c = citt j.17

All this does is set a flag in the bitstream.
If you have a PCM input file where one of the above types of
(obsolete) emphasis has been applied,
you can set this flag in LAME.
Then the mp3 decoder should de-emphasize the output during playback,
although most decoders ignore this flag.

A better solution would be to apply the de-emphasis with a standalone
utility before encoding,
and then encode without
.B -e. 
.TP
.B -c
Mark the encoded file as being copyrighted.
.TP
.B -o
Mark the encoded file as being a copy. 
.TP
.B -p
Turn on CRC error protection.
.br
It will add a cyclic redundancy check (CRC) code in each frame,
allowing to detect transmission errors that could occur on the
MP3 stream.
However,
it takes 16 bits per frame that would otherwise be used for encoding,
and then will slightly reduce the sound quality. 
.TP
.B \-\-nores
Disable the bit reservoir.
Each frame will then become independent from previous ones,
but the quality will be lower. 
.TP
.B \-\-strictly-enforce-ISO
With this option,
LAME will enforce the 7680 bit limitation on total frame size.
.br
This results in many wasted bits for high bitrate encodings but will
ensure strict ISO compatibility.
This compatibility might be important for hardware players.

.PP
Filter options:
.TP
.B -k
Tells the encoder to use full bandwidth and to disable all filters.
By default,
the encoder uses some highpass filtering at low bitrates,
in order to keep a good quality by giving more bits to more important
frequencies.
.br
Increasing the bandwidth from the default setting might produce
ringing artefacts at low bitrates.
Use with care! 
.TP
.BI \-\-lowpass " freq"
Set a lowpass filtering frequency in kHz.
Frequencies above the specified one will be cutoff. 
.TP
.BI \-\-lowpass-width " freq"
Set the width of the lowpass filter.
The default value is 15% of the lowpass frequency. 
.TP
.BI \-\-highpass " freq"
Set an highpass filtering frequency in kHz.
Frequencies below the specified one will be cutoff. 
.TP
.BI \-\-highpass-width " freq"
Set the width of the highpass filter in kHz.
The default value is 15% of the highpass frequency.
.TP
.BI \-\-resample " sfreq"
.I sfreq
= 8, 11.025, 12, 16, 22.05, 24, 32, 44.1, 48
.br
Select output sampling frequency (only supported for encoding).
.br
If not specified,
LAME will automatically resample the input when using high compression ratios.

.PP
ID3 tag options:
.TP
.BI \-\-tt " title"
audio/song title (max 30 chars for version 1 tag)
.TP
.BI \-\-ta " artist"
audio/song artist (max 30 chars for version 1 tag)
.TP
.BI \-\-tl " album"
audio/song album (max 30 chars for version 1 tag)
.TP
.BI \-\-ty " year"
audio/song year of issue (1 to 9999)
.TP
.BI \-\-tc " comment"
user-defined text (max 30 chars for v1 tag, 28 for v1.1)
.TP
.BI \-\-tn " track"
audio/song track number (1 to 255, creates v1.1 tag)
.TP
.BI \-\-tg " genre"
audio/song genre (name or number in list)
.TP
.B \-\-add-id3v2
force addition of version 2 tag
.TP
.B \-\-id3v1-only
add only a version 1 tag
.TP
.B \-\-id3v2-only
add only a version 2 tag
.TP
.B \-\-space-id3v1
pad version 1 tag with spaces instead of nulls
.TP
.B \-\-pad-id3v2
pad version 2 tag with extra 128 bytes
.TP
.B \-\-genre-list
print alphabetically sorted ID3 genre list and exit
.TP
.B \-\-ignore-tag-errors
ignore errors in values passed for tags, use defaults in case an error occurs

.PP
Analysis options:
.TP
.B \-g
run graphical analysis on <infile>.
<infile> can also be a .mp3 file.
(This feature is a compile time option.
Your binary may for speed reasons be compiled without this.)

.SH ID3 TAGS
LAME is able to embed ID3 v1,
v1.1 or v2 tags inside the encoded MP3 file.
This allows to have some useful information about the music track
included inside the file.
Those data can be read by most MP3 players.

Lame will smartly choose which tags to use.
It will add ID3 v2 tags only if the input comments won't fit in v1
or v1.1 tags,
i.e. if they are more than 30 characters.
In this case,
both v1 and v2 tags will be added,
to ensure reading of tags by MP3 players which are unable to read ID3 v2 tags.

.SH ENCODING MODES
LAME is able to encode your music using one of its 3 encoding modes:
constant bitrate (CBR), average bitrate (ABR) and variable bitrate (VBR).
.TP
.B Constant Bitrate (CBR)
This is the default encoding mode,
and also the most basic.
In this mode,
the bitrate will be the same for the whole file.
It means that each part of your mp3 file will be using the same
number of bits.
The musical passage being a difficult one to encode or an easy one,
the encoder will use the same bitrate,
so the quality of your mp3 is variable.
Complex parts will be of a lower quality than the easiest ones.
The main advantage is that the final files size won't change and
can be accurately predicted.
.TP
.B Average Bitrate (ABR)
In this mode,
you choose the encoder will maintain an average bitrate while using
higher bitrates for the parts of your music that need more bits.
The result will be of higher quality than CBR encoding but the
average file size will remain predictable,
so this mode is highly recommended over CBR.
This encoding mode is similar to what is referred as vbr in AAC or
Liquid Audio (2 other compression technologies).
.TP
.B Variable bitrate (VBR)
In this mode,
you choose the desired quality on a scale from 9 (lowest
quality/biggest distortion) to 0 (highest quality/lowest distortion).
Then encoder tries to maintain the given quality in the whole file by
choosing the optimal number of bits to spend for each part of your music.
The main advantage is that you are able to specify the quality level that
you want to reach,
but the inconvenient is that the final file size is totally unpredictable.

.SH PRESETS
The
.B \-\-preset
switches are designed to provide the highest possible quality.

They have for the most part been subject to and tuned via rigorous double blind
listening tests to verify and achieve this objective.

These are continually updated to coincide with the latest developments that
occur and as a result should provide you with nearly the best quality
currently possible from LAME.

To activate these presets:
.PP
For VBR modes (generally highest quality):
.TP
.B \-\-preset medium
This preset should provide near transparency to most people on most music.
.TP
.B \-\-preset standard
This preset should generally be transparent to most people on most music and
is already quite high in quality.
.TP
.B \-\-preset extreme
If you have extremely good hearing and similar equipment,
this preset will generally provide slightly higher quality than the
.B standard
mode.
.PP
For CBR 320kbps (highest quality possible from the
.B \-\-preset
switches):
.TP
.B \-\-preset insane
This preset will usually be overkill for most people and most situations,
but if you must have the absolute highest quality with no regard to filesize,
this is the way to go.
.PP
For ABR modes (high quality per given bitrate but not as high as VBR):
.TP
.B \-\-preset " kbps"
Using this preset will usually give you good quality at a specified bitrate.
Depending on the bitrate entered,
this preset will determine the optimal settings for that particular situation.
While this approach works,
it is not nearly as flexible as VBR,
and usually will not attain the same level of quality as VBR at higher bitrates.
.PP
The following options are also available for the corresponding profiles:
.PP
.B fast standard|extreme|insane
.br
.B cbr " kbps"
.PP
.TP
.B fast
Enables the new fast VBR for a particular profile.
The disadvantage to the speed switch is that often times the bitrate will be
slightly higher than with the normal mode and quality may be slightly lower also.
.TP
.B cbr
If you use the ABR mode (read above) with a significant bitrate such as 80,
96,
112,
128,
160,
192,
224,
256,
320,
you can use the
.B cbr
option to force CBR mode encoding instead of the standard ABR mode.
ABR does provide higher quality but CBR may be useful in situations such as when
streaming an MP3 over the Internet may be important.


.SH EXAMPLES
.LP
Fixed bit rate jstereo 128kbs encoding:
.IP
.B lame
.I sample.wav sample.mp3

.LP
Fixed bit rate jstereo 128 kbps encoding, highest quality (recommended):
.IP
.B lame \-h
.I sample.wav sample.mp3

.LP
Fixed bit rate jstereo 112 kbps encoding:
.IP
.B lame \-b
.I 112 sample.wav sample.mp3

.LP
To disable joint stereo encoding (slightly faster,
but less quality at bitrates <= 128 kbps):
.IP
.B lame \-m
.I s sample.wav sample.mp3

.LP
Fast encode,
low quality (no psycho-acoustics):
.IP
.B lame \-f
.I sample.wav sample.mp3

.LP
Variable bitrate (use \-V n to adjust quality/filesize):
.IP
.B lame \-h \-V
.I 6 sample.wav sample.mp3

.LP
Streaming mono 22.05 kHz raw pcm, 24 kbps output:
.IP
.B cat
.I inputfile
.B | lame \-r \-m
.I m
.B \-b
.I 24
.B \-s
.I 22.05 \- \-
.B >
.I output

.LP
Streaming mono 44.1 kHz raw pcm,
with downsampling to 22.05 kHz:
.IP
.B cat
.I inputfile
.B | lame \-r \-m
.I m
.B \-b
.I 24
.B \-\-resample
.I 22.05 \- \-
.B >
.I output

.LP
Encode with the
.B fast standard
preset:
.IP
.B lame \-\-preset fast standard
.I sample.wav sample.mp3

.SH BUGS
.PP
Probably there are some.
.SH SEE ALSO
.BR mpg123 (1) ,
.BR madplay (1) ,
.BR sox (1)
.SH AUTHORS
.nf
LAME originally developed by Mike Cheng and now maintained by
Mark Taylor.  GPSYCHO psycho-acoustic model by Mark Taylor.
(http://www.mp3dev.org/).
mpglib by Michael Hipp
Manual page by William Schelter, Nils Faerber, Alexander Leidinger.
Small fixes on the manual page by Rogerio Brito.
.f