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lavpipe




SYNOPSIS

       lavpipe [-o num] [-n num] pipe-list


DESCRIPTION

       lavpipe  reads  a  little  script file that I called 'pipe
       list' and 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 mpeg2enc(1) or yuv2lav(1)).


OPTIONS

       The  command  line options allow to only 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.

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

       -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 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).

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

       -?     Display a synopsis of the command syntax.


EXAMPLES

       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

       ing list (see below).

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

       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.

       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.

       Now follows the source list:

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

       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:
              lav2yuv -o $o -f $n input.avi

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

       And  after  this  you can append as many sequence descrip­
       tions as needed. Each of them is built up as follows:

       num    The number of frames that this sequence will  last.

       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
              that  reads num input streams and writes one output
              stream, combining its inputs. Optionally, the  fil­
              ter  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
              README.lavpipe or the documentation for the  filter
              programs  (if  available).  An example filter could
              look like this:
              transist.flt -o 0 -O 255 -s $o -n $n -d 50
              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:
              -

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

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


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.


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.
       But I want to note that it is very well possible to  write

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


SEE ALSO

       lav2yuv(1),     lavplay(1),     lavrec(1),    mpeg2enc(1),
       yuv2lav(1), yuvscaler(1)

MJPEG Linux Square         2 June 2001                 lavpipe(1)

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