mpeg2enc.1

Motion JPEG编解码器源代码

.TH "mpeg2enc" "1" "25 Aug 2002" "MJPEG Tools Team" "MJPEG tools manual"

.SH "NAME"
mpeg2enc \- MPEG-1/2 encoder

.SH "SYNOPSIS"
.B mpeg2enc
.RB [ -v | --verbose
.IR num ]
.RB [ -M | --multi-thread
.IR num_CPU ]
.RB [ -f | --format
.IR mpeg_profile ]
.RB [ -b | --video-bitrate
.IR bitrate_kbps ]
.RB [ -V | --video-buffer
.IR video_buf_size_kB ]
.RB [ -T | --target-still-size
.IR still_size_kB ] 
.RB [ -q | --quantization
.IR quantization ]
.RB [ -r | --motion-search-radius
.IR motion_search_radius ]
.RB [ -Q | --quantization-reduction
.IR \-4.0..5.0 ]
.RB [ -X | --quant-reduction-max-var
.IR 0.0 .. 2500.0]
.RB [ -p | --3-2-pulldown ]
.RB [ -I | --interlace-mode
.IR 0|1|2 ]
.RB [ -s | --sequence-header-every-gop ]
.RB [ -g | --min-gop-size
.IR min_gop_size ]
.RB [ -G | --max-gop-size
.IR max_gop_size ]
.RB [ -P | --force-b-b-p ]
.RB [ -n | --video-norm
.IR n|p|s ]
.RB [ -F | --frame-rate
.IR frame_rate_code ]
.RB [ -a | --aspect
.IR aspect_ratio_code ]
.RB [ -z | --playback-field-order
.IR b|t ]
.RB [ -4 | --reduction-4x4
.IR 1..4 ]
.RB [ -2 | --reduction-2x2
.IR 1..4 ]
.RB [ -S | --sequence-length
.IR size_MB ]
.RB [ -B | --nonvideo-bitrate
.IR bitrate_kbps ]
.RB [ -N | --reduce-hf
.IR 0.0..2.0 ]
.RB [ -D | --intra_dc_prec
.IR 8..11 ]
.RB [ -H | --keep-hf ]
.RB [ -d | --no-dummy-svcd-SOF ]
.RB [ -C | --correct-svcd-hds ]
.RB [ --no-constraints ]
.RB [ -K | --custom-quant-matrices
.IR kvcd|tmpgenc|default|hi-res|file=inputfile|help ]
.RB [ -E | --unit-coeff-elim
.IR -40..40 ]
.RB [ -R | --b-per-refframe
.IR 0..2 ]
.RB [ --no-altscan-mpeg2 ]
.RB [ --dualprime-mpeg2 ]
.RB [ -u | --cbr ]
.RB [ -? | --help ]
.B -o|--output
.I filename

.SH "DESCRIPTION"
mpeg2enc is heavily enhanced derivative of the MPEG Software
Simulation Group's MPEG-2 reference encoder.  It accepts streams in a
simple planar YUV format "YUV4MPEG" produced by the \fBlav2yuv\fP and
related filters (e.g. \fByuvscaler\fP(1)) from the \fBmjpegtools\fP(1)
package.  An output plug-in to the \fBmpeg2dec\fP(1) MPEG decoder is
available to permit its use in transcoding applications. The encoder
currently fully supports the generation of elementary MPEG-1,
progressive and interlaced frame MPEG-2 streams.  Field encoded MPEG-2
is also possible but is not currently maintained or supported.

For most purposes this elementary stream output will need to be
multiplexed with one or more audio streams into a program/systems stream
using the
.BR mplex (1)
tool.

Note that although this manual page aims to explain how mpeg2enc can
be used effectively it is not intended as an introduction to MPEG-1/2
video which is a fairly complex topic in its own right.  The MPEG
video format is a somewhat baroque standard with many many options,
not all of which necessarily easy to explain or even particular useful
in the context of a software encoder.

Much useful practical information for novices can be found in the
mjpeg-HOWTO document that should have been installed with \fBmjpegtools\fP(1)
package.  Further information and useful supporting software can be found
on the mjpegtools web-site:
.br
.IP
\fBhttp://mjpeg.sourceforge.net\fP

.SH "SELECTING THE MPEG PROFILE"
.PP

Set the MPEG profile to use.  The MPEG standards support a vast number
of options.  In practice, different applications of the MPEG format
place additional constraints of the form the MPEG stream.  Setting
this flag selects the kind of stream to produce.

.PP
.BR -f|--format \ 0
        -       Generic MPEG1.
.PP
        A basic MPEG-1 profile that lets most parameters
        be adjusted for particular applications using the other flags.
        Typical applications would be to produce a variable bitrate MPEG-1
        stream with big buffers and a high data-rate software playback
        on a computer.
.PP
.BR -f|--format \ 1 
        -       Standard VCD.
.PP
An MPEG1 profile exactly to the VCD2.0 specification.
Flag settings that would result in a non-standard
stream structure are simply ignored.

.PP
.BR -f|--format \ 2 
        -       User VCD.
.PP
As for profile 2 but bitrate and video buffer size can
be set to non-standard values. Frame size may also be non-standard.
Bit-rate and buffer sizes default to those for standard VCD.
.PP
.BR -f|--format \ 3
        -       Generic MPEG2.
.PP

A basic MPEG-2 profile that lets most parameters be adjusted for
particular applications using the other flags.  Typical applications
would be to produce a MPEG-2 stream with big buffers and long GOP's
for software playback on a computer.

.PP
.BR -f|--format \ 4
        -       Standard SVCD.
.PP
An MPEG-2 profile exactly to the SVCD2.0
specification. Flag settings that would result in a
non-standard stream structure are simply ignored.
.PP
.BR -f|--format \ 5
        -       Non-standard SVCD.
.PP
As for profile 4 but bitrate, video
buffer size, GOP sizes and structure can be set to
non-standard values. Frame size may also be non-standard.
Bit-rate and buffer sizes default to those for standard SVCD.
.PP
.BR -f|--format \ 6
        -       VCD Stills sequence.
.PP
Encodes the special style of MPEG stream
used for still images on VCDs.  To use this profile you must
set the target size you wish to compress the images to using the
-T flag.   Reasonable values are around 35KB for standard resolution
stills (352 wide) and 120KB for high resolution stills (704 wide).
.PP
.BR -f|--format \ 7
        -       SVCD Stills sequence.
.PP
Encodes the special style of MPEG stream
used for still images on SVCDs.  Both standard (480 wide) and high
resolution (704 wide) images are supported. As with VCD stills you
select how big each compressed still should be using the -T flag.
.PP
.BR -f|--format \ 8
        -       DVD MPEG-2 for 'dvdauthor'
.PP
This version adds special dummy navigation packets into the output stream
that the dvdauthor tool fills in to make a proper .VOB for authoring.
Bit-rate defaults to 7500kbps, buffer sizes to the maximum
permitted by the DVD specification.
.PP
.BR -f|--format \ 9
        -       DVD MPEG-2. 
.PP
Just a very basic implementation. Useful with DXR2 board and similar
hardware that can decode MPEG-2 only if it is presented in a DVD like
form.  Bit-rate defaults to 7500kbps, buffer sizes to the maximum
permitted by the DVD specification.
.SH "GENERAL FUNCTION LETTERS"
.PP
.BR -v|--verbose \ num
.PP
Set verbosity level to num.  0 = warnings and errors only, 1 =
information as well, 2=really verbose.
.PP
.BR -K|--custom-quant-matrices \fBkvcd\fP | \fBtmpgenc\fP | \fBdefault\fP | \fBhi-res\fP | \fBfile=\fPinputfile | \fBhelp\fP
.PP
Specify which quantization matrices to use instead of the defaults
(which can be specified by using "-K default").   Using "-K hi-res" is
identical to using the -H option. The value kvcd uses the Kvcd.Net
matrices from http://www.kvcd.net/; the value tmpgenc invokes the
TMPGEnc matrices from http://www.tmpgenc.net/e_main.html. On average
(this depends on the source material), the tmpgenc tables reduce
the average bitrate by about 10% and the kvcd tables reduce bitrate
by about 16% (compared to the default tables).
.PP
.BR -E|--unit-coeff-elim \ -40..40
.PP
Specify when a special 'unit coefficient elimination' algorithm should
be applied to the encoded picture blocks.  Basically, this procedure
forces blocks of a type that don't carry much information but are
expensive to encode to be simply skipped.  The larger the number the
more potentially visible this skipping is likely to be but the more
compression is boosted.  A negative value means that all coefficients
are zeroed, positive means only texture but not base intensity
coefficients are zeroed.  Values of around 10 or -10 seem to work well
with high quality source material. For noisier material it might be
worth trying 20 or -20.  
.PP Note: if B frames are being encoded this only applies to B frames.
.BR -R|--b-per-refframe \ 0..2
.PP
Specify how many bi-directionally (B type) difference-encoded frames
should be encoded between reference (I or P) frames.  The default is 0
except for VCD encoding where it is 2 B frames as required by the
standard.  Experts differ on how much using B frames improves
compression. In practice unless you have really clean material they
tend to be fairly useless and sometimes even harmful.  Encoding is
significantly faster and uses less memory if no B frames are encoded
and compression is rarely more than marginally worse.

.PP
.BR -?|--help
.PP
Display a synopsis of the command syntax.
.SH "FUNCTION LETTERS ADJUSTING THE SELECTED PROFILE"

N.b. If the profile you have selected sets particular values
for these parameters it will over-ride these adjustment flags.
In particular, there is almost \fInothing\fP that can be 
adjusted for the standard VCD and SVCD profiles.

.PP
.BR -b|--video-bitrate \ num 
.PP
The bitrate of the output video stream in kBits/sec.  The default is
exactly the bitrate required for VCD streams.
If variable bitrate (VBR) mode has been selected (see the
-q option) this is the
.I maximum
bitrate of the stream. \fBNOTE:\fP By default MPEG-2 streams (\fB-f\fP
3, 4, 5, 8 and 9 are VBR.  Use the \fB--cbr\fP option for generating
CBR (Constant Bit Rate) streams.
.PP
.BR -V|--video-buffer \ num
.PP
The maximum video buffer usage required to decode the stream in
KBytes.  The default is 46KB the (tiny) size specified for VCD.  The
size to use for SVCD is the (more reasonable) 230KB.  If you are
encoding for a half-decent software decoder it makes sense to push
this up to 500K or more.
.PP
.BR -T|--target-still-size \ num
.PP
Set the target size for (S)VCD still images in KB.
.PP
.BR -s|--sequence-header-every-gop
.PP
This flag forces the encoder to generate a "sequence header" at the start
of every group-of-pictures.  This is needed by some player hardware to
support fast forward/rewind/random access functions but is a waste of bits
otherwise.

.PP
.BR -d|--no-dummy-svcd-SOF
.PP
The SVCD MPEG-2 profile demands that special "Scan OFfset" which are
(in effect) pointers to the place on the final SVCD disk where the
video for 0.5 and around 5-10 seconds behind and ahead in the stream
is located.  The intended use of this information is to support"Fast
forward/Rewind" functions.  Unfortunately, at the time mpeg2enc
encodes the video it doesn't know where the video is going to finally
end up.  So special dummy "Scan OFfset" values are written which are
intended to be filled in during the creation of the SVCD
image. Currently the GNU vcdimager tool handles this task.  However,
in some circumstances the dummy offsets can cause problems.   This
flags stops mpeg2enc generating them.
.PP
.BR --correct-svcd-hds
.PP
In the official SVCD standards the field in the MPEG-2 header
information that passes on the encoders "recommended" horizontal
resolution to decode the stream to is supposed to take the values 540
(for 4:3 sequences) or 720 (for 16:9 sequences).  In practice many
players don't work unless the value is 480. This flag, forces mpeg2enc
to follow the official standard. It is worth trying if 16:9 sequences
play at 4:3 aspect ratio.
.PP
.BR --no-constraints
.PP
This flag deactivates all constraints for the maximum video samplerate or video resolution. Its purpose is to allow the encoding of unusual resolutions of MPEG-video (e.g. 2200 x 576, 160 degrees FOV VR-theatre MPEG movies), but should be used with care: It can possible circumvent a number of other security checks, and untested settings can cause mpeg2enc to crash in this mode. 
.PP
.BR --no-altscan-mpeg2
.PP
This flag deactivates the use of the 'alternate' macroblock scan pattern for 
MPEG2 encoding.  Normally this pattern is used but a few elderly software 
decoders had bugs relating to this feature.  You should never need to use this flag.
.PP
.BR --dualprime-mpeg2
.PP
MPEG-2 supports a special motion estimation mode (DPME, Dual Prime Motion
Estimation) for I/P-frame only streams that can somewhat improve compression.  
A number of players (both hardware and software) do not support this mode.   
Those players  may or may not be
MPEG-2 compliant depending if DPME is an option or not in the MPEG-2 specs.  
If you need to generate content for  such players (e.g. Ogle or Apple's