lavpipe.1

Motion JPEG编解码器源代码

.TH "lavpipe" "1" "2 June 2001" "MJPEG Linux Square" "MJPEG tools manual"

.SH "NAME"
lavpipe \- creates raw YUV streams from pipe list scripts

.SH "SYNOPSIS"
.B lavpipe
.RB [ -o
.IR num ]
.RB [ -n
.IR num ]
.I pipe-list

.SH "DESCRIPTION"
lavpipe reads a script file called 'pipe list'
that is of a similar structure as the edit lists that
can be fed into lav2yuv.  For info about the pipe list format
see below.

The pipe list defines several video sources and filters
that are combined by lavpipe to produce a single output YUV
stream on stdout (which for example can be compressed and
stored to disk via
.BR mpeg2enc "(1) or " yuv2lav "(1))."

.SH "OPTIONS"
The command line options are used to output a specific
part of the resulting video stream.  That means you can
tell lavpipe how many frames to skip and how many frames
to deliver from that point on.

.TP
.BI "-o " num
This is the frame offset of the output video. The first
.I num
frames of the resulting video simply are neither calculated
nor written to stdout. This value defaults to 0.

.TP
.BI "-n " num
This is the frame count. If the input files or streams defined
in the pipe list script are long enough, the output will be
of exactly
.I num
frames length. A value of 0 means that all frames until the
last one as defined in the pipe list will be written out, as
long as there's some input (0 is the default).

.TP
.I pipe-list
This is name of the pipe list file that lavpipe will 'execute'.
For information about this file's format see below.

.TP
.B -?
Display a synopsis of the command syntax.

.SH "EXAMPLES"

.TP
lavpipe -o 100 -n 25 film.pli
would calculate and output to stdout frames 100 to 124 as
defined in film.pli (in PAL this would be the 5th second of
the film).
.TP
lavpipe input.pli | yuv2lav -q80 output.avi
would save the movie assembled by lavpipe as a single AVI file.

.SH "USAGE"
In this section the format of lavpipe's input files the pipe
list scripts is explained. If you need some examples or a more
detailed tutorial, please read the
.BR mjpegtools "(1) manpage's section about"
.BR "CREATING MOVIE TRANSITIONS" ". and the file"
.I README.lavpipe
that should be included in the distribution.
Also feel free to contact us via the mailing list (see below).

A pipe list contains of two parts: the YUV
.B source list
and after this, as many
.B sequence descriptions
as wanted. It always begins with the following two lines:

.TP
.B LAV Pipe List
This is the first line in every pipe list script. It is used as
a simple test if lavpipe really was given a pipe list script and
not your PhD thesis as input.

.TP
.BR NTSC | PAL
This is the second line in every pipe list and can be either PAL
or NTSC, depending on what video standard you use. I don't remember
if this is used at the moment.

.PP
Now follows the
.BR "source list" :

.TP
.I num
This is the number of input commands. lavpipe will read the next
.I num
lines and interpret them as input stream commands.

.TP
.IR command \ ( num \ times)
This is a valid command line with two variables $o and $n that
will be replaced by lavpipe with the offset and number of frames
that the program has to output. Example:
.br
.B lav2yuv -o $o -f $n input.avi

.PP
.RB "Thus, an example " "source list" " could look like this:"
.br
.B 2
.br
.B lav2yuv -o $o -f $n scene1.avi
.br
.B lav2yuv -o $o -f $n scene2.avi

after this you can append as many
.B sequence descriptions
as needed. Each of them is built up as follows:

.TP
.I num
The number of frames that this sequence will last.

.TP
.I num
The number of inputs that will be used in this sequence.
This number must of course be less than or equal to the
number of inputs that are defined above.

.TP
.IR idx " [" ofs "] (" num " times)"
These are the indices to the sources that are defined
at the beginning of the file (first source is 0) with
an optional frame offset (i.e. sequence starts with
.RI "frame number " ofs " of this input.) - this value"
defaults to 0. Example:
.br
.B 0 150

.TP
.I command
This is a valid command line to a YUV filter tool that reads
.IR num " input streams and writes one output stream, combining"
its inputs. Optionally, the filter tool can be given the two
$o and $n variables that will be replaced by lavpipe as in
the source commands (see above). For further info read
.IR README.lavpipe " or the documentation for the filter"
programs (if available). An example filter could look like this:
.br
.B transist.flt -o 0 -O 255 -s $o -n $n -d 50
.br
And if the sequence only has one input that simply should be
copied to the output, you can use a dash instead of a command line:
.br
.B -

.PP
And here's an example for a complete pipe list that implements
a transistion from scene1.avi to scene2.avi (remove the comments after #):

.B LAV Pipe List
.br
.B PAL
.br
.B 2
.br
.B lav2yuv -o $o -f $n scene1.avi
.br
.B lav2yuv -o $o -f $n scene2.avi
.br
.BR 50   "            # first sequence: 50 frames"
.br
.BR 1   "             #   contains one input:"
.br
.BR "0 0" "           #     scene1.avi, offset 0"
.br
.BR -   "             #   simple output"
.br
.BR 25   "            # second sequence: 25 frames"
.br
.BR 2   "             #   contains two inputs:"
.br
.BR "0 50" "          #     scene1.avi, offset 50"
.br
.BR 1   "             #     scene2.avi, offset 0"
.br
.BR "transist.flt -o 0 -O 255 -s $o -n $n -d 50" " # transistion"
.br
.BR 50   "            # third sequence: 50 frames"
.br
.BR 1   "             #   contains one input:"
.br
.BR "1 25" "          #     scene2.avi, offset 25"
.br
.BR -   "             #   simple output"

.SH "BUGS"
I'm sure there are enough of them. lavpipe often accepts
malformed pipe lists and then writes out a video that was
all but intended - without warning.

.SH "NOTES"
There are also some serious limitations in the system, such
as frame-by-frame processing. But as the goal when writing
lavpipe was the simplicity of the pipeline, other tools will
have to be written to do more interesting tasks.
.br
But I want to note that it is very well possible to write
a pipe list that combines several files, and then use that
pipe list as an input for another pipe list by simply
using the lavpipe command in the source list (see above) -
this can be already used to do some nice things, if you
have some nice filters.

.SH AUTHOR
This man page was written by pHilipp Zabel.
.br
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

.TP
For more info, see our website at
.I http://mjpeg.sourceforge.net

.SH "SEE ALSO"
.BR lav2yuv (1),
.BR lavplay (1),
.BR lavrec (1),
.BR mpeg2enc (1),
.BR yuv2lav (1),
.BR yuvscaler (1)