mpeg2enc.1

Motion JPEG编解码器源代码

DVD player application) you should NOT turn on dualprime-mpeg2!  Surprisingly 
at least one hardware/set-top player is known to be allergic to DPME being 
used.
.PP
.BR -z|--playback-field-order \ b|t
.PP
This flag overrides the field-order specified in the interlacing tag of
the input stream header. (If you need this option, it indicates a problem
in the capturing/encoding process where the temporal order of the two
fields in each frame has been mislabeled. The effect of this is weird
"juddering" when playing back the stream on a TV. Check the mjpeg-howto
for more information about interlacing problems.)
.PP
.SH "OPTION LETTERS CONTROLLING VIDEO PARAMETERS"
.PP
.BR -n|--video-norm \ n|p|s
.PP
Force the input stream to be treated as NTSC|PAL|SECAM regardless of
what the stream header might suggest.  Basically this just sets the
defaults for a bunch of other options.
.PP
.BR -F|--frame-rate \ num
.PP
Set the frame-rate of the output-stream. By default, this value is
inferred from the input header. Currently only the standard
MPEG rates are supported.  Eventually more-or-less arbitrary rates
will be possible.
.br
 0 - illegal
.br
 1 - 24000.0/1001.0 (NTSC 3:2 pulldown converted FILM)
.br
 2 - 24.0 (NATIVE FILM)
.br
 3 - 25.0 (PAL/SECAM VIDEO / converted FILM)
.br
 4 - 30000.0/1001.0 (NTSC VIDEO)
.br
 5 - 30.0
.br
 6 - 50.0 (PAL FIELD RATE)
.br
 7 - 60000.0/1001.0 (NTSC FIELD RATE)
.br
 8 - 60.0
.br
.PP
.BR -a|--aspect \ num
.PP
Set the playback aspect ratio code of the encoded video. By default, this 
value is inferred from the input header.
.br
 1 - 1  - 1:1 display
.br
 2 - 2  - 4:3 display
.br
 3 - 3  - 16:9 display
.br
 4 - 4  - 2.21:1 display
.IP
For MPEG-2 the specified aspect ratios are used directly. For MPEG-1
mpeg2enc infers the MPEG-1 pixel aspect code from the video norm
specified and the specified playback aspect ratio.

.PP
.BR -p|--3-2-pulldown
.PP
Setting -p only makes sense for 24frame/sec Movie source material.  It sets
flags in the output stream that tell the decoder to play the movie as
NTSC 60field/sec video using "3:2 pulldown".  This is vastly more
efficient than encoding as 60field/sec video.  The classic application
is to transcode a PAL-encoded movie (24fps played too fast at 25 fps!)
into NTSC (see the -f flag).

.SH "OPTION LETTERS FOR CONTROLLING COMPRESSION AND SPEED"
.PP
.BR -M|--multi-thread \ num_CPU
.PP
MPEG encoding is a task that can be split over a small number of CPU's
quite efficiently.  Mpeg2enc can be internally set to split major
processing tasks between a number of concurrent threads.   This flag
adjusts the multi-threading to the optimum to utilise the specified
number of CPU's.
.PP
It should be noted that even with 1 CPU present \fIsome\fR
multi-threading is performed: frame input takes place in parallel with
encoding.  The default -M value is 1.  This allows good performance to 
be achieved when when a
seperate machine is being used for pre-processing (decoding from
MJPEG, scaling, denoising etc) with the final result pipe to mpeg2enc
(e.g. using rsh or ssh).
.PP
Setting -M 0 disables all multithreading.  This is sometimes useful
for debugging or to achieve maximum CPU efficiency on a shared
machine. Setting -M 3 on a dual-CPU machine will produce slightly
faster results than -M 2 at the price of slightly less CPU efficiency.
This is useful if nothing else needs to be done on the encoding
machine.  In practice there is little point setting -M greater than 4
even if the CPU's are available due to the fairly coarse-grained
parallelism used.  Indeed there is a hardcoded limit of 4 worker threads.
.PP
The default has been changed to be 0 instead of 1 to avoid the crash at
end of encoding:
.nf

INFO: [mpeg2enc] Signaling last frame = 499
mpeg2enc: seqencoder.cc:433: void SeqEncoder::EncodeStream(): Assertion `pass1coded.size() == 0' failed.
Abort
.fi
.PP
.BR -q|--quantization \ 1 .. 31
.PP
Minimum quantization of the output stream.  Quantisation controls the
precision with which image information is encoded.  The lower the
number the higher the quality but the greater the required data-rate.
\fBNOTE:\fP on IA32 systems it is possible to cause artifacting by setting
the value too low (3 or less) due to arithmetic overflow/truncation in the
DCT/iDCT routines.
If this option is set a 
.I variable bitrate 
stream is produced.  This is more efficient
but variable bitrate MPEG-1 cannot be played by some hardware
decoders and is rejected by some DVD authoring packages.  If you intend 
to use a software decoder you'd be insane not to use variable bitrate.
.sp
If this option is set without a maximum bitrate being specified then
quantization is fixed at the specified value.  It should be noted that not
specifying a bitrate is probably an error and may produce unexpected results.
.sp
For MPEG-2 streams a default of 8 is used if \fB-q\fP is not explicitly given.
To force constant bitrate streams use \fB--cbr\fP and \fB-b NOT -q\fP!
.PP
.BR -I|--interlace-mode \ 0|1|2
.PP
Set the sequence picture structure and block encoding type for MPEG-2 streams.
By default, this value is inferred from the interlacing tag of the input
stream. Setting 0 encodes frame-by-frame with support for interlaced video
turned off, and specifies that progressive chroma subsampling has been used.
Setting 1 encodes frame-by-frame with interlace-adapted motion compensation
and block encoding, and specifies that interlaced chroma subsampling has
been used. Setting 2 encodes interlaced material field-by-field, which 
will produce more accurate results for highly textured interlaced
material with lots of motion, at the expense of generally less efficiency.
.IP
This setting should match the interlaced-ness of the input stream, otherwise
chroma artifacts may be generated when the MPEG stream is played back.
.PP
.BR -g|--min-gop-size \ num
.PP
.BR -G|--max-gop-size \ num
.PP
These flags set the minimum and maximum group-of-picture (GOP) size
for the output MPEG stream.  By default both are set to 12 to suit VCD
encoding.  If the two values are not identical mpeg2enc applies a
simple scene-change detection procedure to try to select GOP sizes
that ensure big changes of image coincide with the fully-encoded
I-frame starting a new GOP.  This can help prevent transient
"blockiness".  For VCD/SVCD/DVD the largest GOP size is 15 for PAL or 18 for
NTSC.  Reasonable minimum GOP sizes are 6 or 9.  A larger GOP size can
help reduce the bitrate required for a given quality.  However, this
really only applies to high-quality source material with little noise
(e.g. digital video).  For broadcast material there is little point
setting GOP size much beyond 21 or 24.  Even with good source material
diminishing returns set in quite rapidly.

Note: Mpeg2enc is currently hard-wired to produce 2 B frames between
each I/P frame unless the GOP size forces less.  This is reasonable
for medium to high bitrates (>= 1Mbps) but probably sub-optimal for
low-bitrate encoding.
.PP
.BR -c|--closed-GOPs
.PP
Setting this flag causes the encoder to generate only "closed" GOPs
(Groups of Pictures) that can be decoded without reference to their
predecessor.  This is useful for streams that are supposed to be used
in multi-angle DVD's and applications where more easily edittable MPEG
is required.
.PP
.BR -P|--force-b-b-p
.PP
This flag forces the GOP size selection to choose sizes 
that ensure 2 B frames appear between adjacent I/P frames.
Several common MPEG-1 decoders can't handle streams where less than
2 B-frames appear between I/P frames.
.PP
.BR -Q|--quantization-reduction \ -4.0..5.0 
.PP
This flag sets the amount quantization is reduced for
blocks containing large amounts of sharp image detail.
Large values produces efficient use of bits but may
cause visible artifacting around detailed sections.
With noisy source material this option may cause
a "swimming" effect on textured backgrounds as the noise cause the 
quantization of blocks to be boosted at random.  The default is 0.0 (off).
See also the \-X option.
.PP
.BR -X|--quant-reduction-max-var \ 0.0..2500.0
.PP
Luma variance below which quantization boost (-Q) is activated.
.PP
.BR -r|--motion-search-radius \ num
.PP
This flag sets the motion estimation search radius.  For most
purposes the default (16) should be just fine.  For high-resolution
MPEG-2 and active scenes it may be worth bumping it up.  However, this
will make encoding significantly slower.  There is little point
reducing the radius.  Speed gains are not huge and the impact on quality
can be marked.
.PP
.BR -4|--reduction-4x4 \ 1..4
.PP
.BR -2|--reduction-2x2 \ 1..4
.PP
These options control how radical the encoder is in throwing away
apparently poor candidate estimates during motion estimation.  A
setting of 1 means very few blocks are discarded early which makes for
slow encoding but quality as good as it gets. A setting of 4 makes for
fast encoding but can impact quality.  The -4 flag controls discarding
during the initial 4*4 sub-sampled search stage, the -2 flag controls
discarding during the secondary 2*2 sub-sampled stage.
.IP
These flags are useful as the speed quality trade-off is markedly
different depending on which CPU you have.  On modern machines the
impact on speed is around a factor 2 on older machines a factor 3.
The impact on quality is around 10% quantization (0.2 of a bit of
precision in encoding textures).  For most purposes the default
settings will be fine.  However on P-III Katmai etc -4 2 -2 1 gives a
good near-optimum quality setting with reasonably speed.
.PP
.BR -N|--reduce-hf \ num
.PP
Setting this flag adjusts the way texture detail is quantized to
reduce the precision with which of high-frequency information
encoded. This is very useful for
.I mildly
noisy sources.  If you have really noisy material the filtering tools
available in mjpegtools are a much better bet.  The specified number
must be in the range 0.0 to 2.0 gives the maxium quantization boost.
A useful number to use would be 1.5 or 1.0.
.PP
.BR -H|--keep-hf
.PP
Setting this flag makes the encoder encode as much high-frequency information
as possible.   This is a good setting for maximising quality at VCD
resolution with good quality low-noise source material.  It can also help
with "swimmy" material if you can spare the bitrate!
.PP
.BR -D| --intra_dc_prec \ num
.PP 
Specifies the precision of the DC component. The default is 9. Most 
commercial DVDs use 10. Using 9 instead saves a few bits. Using 10 might
help to avoid looking larger areas of nearly the same color blocky. 
A value of 11 is only valid at the next MPEG-2 profile/level so it's not
a currently meaningful value to use.

.SH "OPTION LETTERS FOR CHUNKING THE OUTPUT STREAM"
.PP
.BR -S|--sequence-length \ num
.PP
This flag allows the target size of individual sequences in the final
multiplexed stream to be set in MBytes. If set  mpeg2enc keeps track
of how large the eventual stream is getting and inserts a sequence
split (actually: sequence end / sequence start) into the output stream
each time it reaches the specified limit.  The multiplexer \fBmplex\fP(1) can
recognise these splits and start a new multiplexed output file each time
it encounters one.   In this way it is easy to automatically ensure
each component sequence file can be burnt onto a CD-R and still be
played as a stand-alone MPEG sequence.   For the SVCD and VCD profiles
the default target sequence length is 700M bytes. For other profiles the
default is that sequence length is unlimited.
.PP
.BR -B|--nonvideo-bitrate \ num
.PP
Since mpeg2enc can't read minds it cannot know in advance what other
material will be multiplexed with the output video stream.  Thus to
get its calculations of where to insert split point right it needs to be
told the combined data-rate of the other material that is eventually to
be multiplexed with the video.
This flag allows this rate to be specified in K bits/sec.

A good rule of thumb is to use the total rate of all the other streams
plus 1% of the total rate including video.
.PP
.BR -u|--cbr
.PP
Force the use of Constant Bit Rate encoding.  Less than optimal (and 
inefficient in almost all cases)
but some folks insist on it. \fBNOTE:\fP this \fBdisables\fP (overrides)
the use of the \fB-q\fP option!
.sp
It is an error to use this option and not specify a bitrate using \fB-b\fP
since a constant bitrate of 0 makes no sense.
.SH "SSE, 3D-Now!, MMX"!
mpeg2enc makes extensive use of these SIMD instruction set extension
on x86 family CPU's.  The routines used are determined dynamically at
run-time.  It should be noted that using SSE requires operating system
support.  Old 2.2.x Linux kernels (unless patched ones like RedHat) do
not have this and so SSE, although physically present, won't be activated.
.SH "BUGS"
There should be an option to force GOP sizes that permit 2 B frames
between I/P frames.  Some decoders (even software)  can't handle the case
where I/P frames come back to back or with only 1 B frame between them.

There needs to be a facility for writing dummy user-data fields so
that the multiplexer/imager can insert forward/backward pointers when
muxing/imaging an SVCD.

Is there some kind soul out there with source-code for a good SSE
(not MMX) DCT and iDCT?
.SH AUTHOR
This man page was written by Andrew Stevens.
If you have questions, remarks, problems or you just want to contact
the developers, the main mailing list for the MJPEG-tools is:
  \fImjpeg\[e-mail]\fP

For more info, see our website at
  \fIhttp://mjpeg.sourceforge.net

.SH "SEE ALSO"
.BR mplex "(1), " mp2enc "(1), " lavrec "(1), " lavplay "(1), "
.BR lav2yuv "(1), " lav2wav "(1), " yuvscaler "(1), " yuvdenoise "(1), " y4mdenoise "(1), " mjpegtools "(1)"