usage.txt

LAME无疑是目前最优秀的MP3编码软件

streams.  




=======================================================================
copyright
=======================================================================
-c   

mark the encoded file as copyrighted



=======================================================================
clipping detection
=======================================================================
--clipdetect

Enable --replaygain-accurate and print a message whether clipping 
occurs and how far in dB the waveform is from full scale.

This option is not usable if the MP3 decoder was _explicitly_ disabled 
in the build of LAME.

See also: --replaygain-accurate



=======================================================================
block type control
=======================================================================
-d 

Allows the left and right channels to use different block types.
Normally this is not allowed, only because the FhG encoder does
not seem to allow it either.  If anyone finds a sample where -d
produces better results, let me know.  ([e-mail])


=======================================================================
mpglib decode capability
=======================================================================
--decode 

This just uses LAME's mpg123/mpglib interface to decode an MP3 file to
a wav file.  The input file can be any input type supported by
encoding, including .mp3 (layers 1, 2 and 3) and .ogg.  

If -t is used (disable wav header), LAME will output
raw pcm in native endian format (use -x to swap bytes).

This option is not usable if the MP3 decoder was _explicitly_ disabled
in the build of LAME.


=======================================================================
de-emphasis
=======================================================================
-e  n/5/c   

  n = (none, default)
  5 = 0/15 microseconds
  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 -e.  



=======================================================================
fast mode
=======================================================================
-f   

Same as -q 7.  

NOT RECOMMENDED.  Use when encoding speed is critical and encoding
quality does not matter.  Disable noise shaping.  Psycho acoustics are
used only for bit allocation and pre-echo detection.

=======================================================================
strictly enforce VBR minimum bitrate
=======================================================================
-F   

strictly enforce VBR minimum bitrate.  With out this optioni, the minimum
bitrate will be ignored for passages of analog silence.



=======================================================================
free format bitstreams
=======================================================================
--freeformat   

LAME will produce a fixed bitrate, free format bitstream.
User must specify the desired bitrate in kbps, which can
be any integer between 8 and 640.

Not supported by most decoders.  Complient decoders (of which there
are few) are only required to support up to 320 kbps.  

Decoders which can handle free format:

                     supports up to
MAD                      640 kbps
"lame --decode"          550 kbps  
Freeamp:                 440 kbps
l3dec:                   310 kbps





=======================================================================
high quality
=======================================================================
-h

use some quality improvements.  The same as -q 2.



=======================================================================
keep all frequencies
=======================================================================
-k   

keep all frequencies.  (Disable all filters)

LAME will automatically apply various types of lowpass filters.  This
is because the high frequency coefficients can take up a lot of bits
that would be better used for lower, more important frequencies.

-k will disable all lowpass filtering.  Not recommended.



=======================================================================
Modes:
=======================================================================

-m m           mono
-m s           stereo
-m j           joint stereo
-m f           forced mid/side stereo
-m d           dual (independent) channels
-m i           intensity stereo
-m a           auto

MONO is the default mode for mono input files.  If "-m m" is specified
for a stereo input file, the two channels will be averaged into a mono
signal.  

STEREO

JOINT STEREO is the default mode for stereo files with fixed bitrates of
128 kbps or less.  At higher fixed bitrates, the default is stereo.
For VBR encoding, jstereo is the default for VBR_q >4, and stereo
is the default for VBR_q <=4.  You can override all of these defaults
by specifing the mode on the command line.  

jstereo means the encoder can use (on a frame by frame bases) either
regular stereo (just encode left and right channels independently)
or mid/side stereo.  In mid/side stereo, the mid (L+R) and side (L-R)
channels are encoded, and more bits are allocated to the mid channel
than the side channel.  This will effectively increase the bandwidth
if the signal does not have too much stereo separation.  

Mid/side stereo is basically a trick to increase bandwidth.  At 128 kbps,
it is clearly worth while.  At higher bitrates it is less useful.

For truly mono content, use -m m, which will automatically down
sample your input file to mono.  This will produce 30% better results
over -m j.  

Using mid/side stereo inappropriately can result in audible
compression artifacts.  To much switching between mid/side and regular
stereo can also sound bad.  To determine when to switch to mid/side
stereo, LAME uses a much more sophisticated algorithm than that
described in the ISO documentation.

FORCED MID/SIDE STEREO forces all frames to be encoded mid/side stereo.  It 
should only be used if you are sure every frame of the input file
has very little stereo seperation.  

DUAL CHANNELS   Not supported.

INTENSITY STEREO

AUTO

Auto select should select (if input is stereo)
          8 kbps   Mono
     16- 96 kbps   Intensity Stereo (if available, otherwise Joint Stereo)
    112-128 kbps   Joint Stereo -mj
    160-192 kbps   -mj with variable mid/side threshold
    224-320 kbps   Independent Stereo -ms



=======================================================================
MP3 input file
=======================================================================
--mp3input

Assume the input file is a MP3 file.  LAME will decode the input file
before re-encoding it.  Since MP3 is a lossy format, this is 
not recommended in general.  But it is useful for creating low bitrate
mp3s from high bitrate mp3s.  If the filename ends in ".mp3" LAME will assume
it is an MP3.  For stdin or MP3 files which dont end in .mp3 you need
to use this switch.


=======================================================================
disable historgram display
=======================================================================
--nohist

By default, LAME will display a bitrate histogram while producing
VBR mp3 files.  This will disable that feature.


=======================================================================
disable ReplayGain analysis
=======================================================================
--noreplaygain

By default ReplayGain analysis is enabled. This switch disables it.

See also: --replaygain-accurate, --replaygain-fast


=======================================================================
disable short blocks
=======================================================================
--noshort

Encode all frames using long blocks.  NOT RECOMMENDED.  For
testing purposes only.  



=======================================================================
non-original
=======================================================================
-o   

mark the encoded file as a copy



=======================================================================
CRC error protection
=======================================================================
-p  

turn on CRC error protection.  
Yes this really does work correctly in LAME.  However, it takes 
16 bits per frame that would otherwise be used for encoding.


=======================================================================
algorithm quality selection
=======================================================================
-q n  

Bitrate is of course the main influence on quality.  The higher the
bitrate, the higher the quality.  But for a given bitrate,
we have a choice of algorithms to determine the best
scalefactors and huffman encoding (noise shaping).

-q 0:  use slowest & best possible version of all algorithms.

-q 2:  recommended.  Same as -h.  -q 0 and -q 1 are slow and may not produce 
       significantly higher quality.  

-q 5:  default value.  Good speed, reasonable quality